Inconsistent idle surge
 

The surge has a range from 800-1200 rpm. Perhaps this is a clue: I can get the surge to stop if I give it small amounts of revving, maybe to around 1500 rpm and then let off slowly. It will then have a solid idle at around 800+- 50, and the AFR is at 13.6 to 14.2. When it surges, obviously the AFR goes up and down. Also, the surge usually doesnt occur until fully warmed up. All fuel pressures spec out. If I try to adjust the CO screw and or the idle screw to tune to surge away, it will work, but its only temporary, as the surge resurfaces everytime!! The only thing I havent done is presurize the intake tract...I will be doing it as soon as i can find a proper size adapter (anyone got tips for that?). I keep thinking it must be a vacuum leak but Ive triple checked everything vacuum related and have come up emtpy handed. I also keep hearing about a rich condition causing a surge? Ive also tried playing with the timing at idle. Latest thing Ive done was remove the fuel head and its plunger for inspection, thinking it may be sticking, but all was good and it had no effect. Valves just adjusted and leak down performed (5-8% across the board).


Background: Decel valve was removed years ago and lines were capped. AAR still installed and functions correctly. About 6 months ago, injector blocks were changed along with their gaskets, recirc valve resealed, new plug wires/plugs/cap/rotor, diassembled dizzy and relubed all components, WUR rebuilt by Leask, all new O rings throughout, a few injectors replaced due to questionable spray pattern, all new vac lines, timing is spot on (26@4k rpm), new filters blah blah blah and the car ran rather great! The K27HFS that was installed at the time failed so the car was down for a bit. A stock 3LDZ was reinstalled and the surge was noticed immediately. Triple checked all connections and found nothing wrong. I suspected the compressor side of the turbo was leaking (due to oil seepage at the bottom of the compressor to center housing mating) so I didnt worry about it as the 3LDZ was temporary. I then installed a GT35R and the problem still exists.

On a positive note, the car kicks butt with the GT35 and with the .8 spring in the wastegate, I see 7.5-.8 bar on the Andial gauge. Ive only taken the car up to about 5k rpm and not 100% full throttle thus far. Here's a pic for the hell of it:
http://i10.photobucket.com/albums/a1...ef9/turbo1.jpg

Same problem here what helped was removal of the aav .you should read my posts had the same exact problem .one of my posts showthe tool needed to presurize the intake.
Good luck

I think I may have come across your thread already. Is the AAV the same as the 'decel valve'? I realize there are multiple names for the same part.

The AAR is still installed but it looks to be functioning correctly (fully closed when warmed up) and even so, pinching the hose while the car is warm and idling makes no difference. What really gets me is I can get the surging to stop every single time if I play with the gas pedal a little bit.

same excat problem I had.the AAV is the gold disc on the left when you look at the engine from the back under the I/C . from your pic it looks like it is blocked.

With all the confusion and multiple names for the deceleration valve, AAV, and AAR I just call them golden saucer valves now.
The early 930's had 2 golden saucer valves, one has a small vacuum line that opens it during times of high intake manifold vacuum and that one is the deceleration valve or vacuum limiter valve.

The other saucer valve doesn't have a small vacuum line that operates it and only the 2 larger hoses that bypass the throttle body. That one is called the AAV most of the time and the late eightee's 930's do not have one of those, thankfully.

The last throttle body bypass valve is the AAR that is cast aluminum and looks nothing like a golden saucer valve. This one bypasses air around the TB when the engine is cold so the idle is raised. I call that one the aux. airslide valve to try and make it less confusing.

Your engine is running a little rich when idle oscillates while warmed up. There are alot of things that could cause that and the simplist thing may be the air sensor plate pivot bearing is just a little stiff or gummed up and not raising back up to where it should at idle.
Could be a vacuum leak(s) and could be your control pressure regulator being inconsistant too.

Next time you have the rear tin off you might want to take the time to strip off all the rust with phosphoric acid, sand or bead blasting, or wire brushes on a die grinder... whatever works for you. Then paint it with 1500 degree header paint or barbecue paint.
It'll stink when the paint burns off right above the turbine housing at first but will make the tin last longer and look alot better down the road.
They are getting very expensive for a piece of stamped out and spot welded sheet metal and not easy to find when they rust away.

JFairman said: "Your engine is running a little rich when idle oscillates while warmed up. There are alot of things that could cause that and the simplist thing may be the air sensor plate pivot bearing is just a little stiff or gummed up and not raising back up to where it should at idle."

Q: How could I go about "unstiffening" or "ungumming" the pivot bearing? Thanks

googd question would not mind cleaning this as well . where and how is this done?
Thanks

ertech: Car only has the aux air slide valve, NO gold discs. Your issue may have been the same but the cause here is different.

Jfairman: Air sensor pivot has been de-gummed with carb cleaner. I did that when I removed the entire unit and separated the fuel dist. from the housing. There was some varnish around the pivot, but operation was still very smooth. I completely flushed that area out and the pivot moves just as freely as before, NO change in surge was noted.

Vacuum leaks to me would indicate a lean condition at idle? Correct or not? If so, how does that conicide with a rich condition surge?

Inconsistent control pressure regulator? You mean faulty WUR? Been rebuilt by Leask less than a year ago, and it ran fine after the install. I guess it could go bad, but pretty unlikely. Obviously though, I wont rule anything out.

What REALLY gets me is I can stop the surge if I play with the gas pedal a little bit. A slight rev to around 1500rpm and let off a little slowly it will idle ROCK SOLID like a normal car.

Hmmmm.....mysterious, especially since you can get it to stop that nasty symptom by revving a bit and SLOWLY letting off the throttle. Sounds like something in the throttle body itself, maybe gummed up and not letting the throttle valve close completely, or an obstruction in one of the vacuum or bypass air ports in the TB. Try pulling off the two vacuum hoses from the TB, as well as the idle adjustment screw...and shooting some carb cleaner in there. Just a long shot idea, I admit.....

Oh...when's the last time you ran any fuel injection cleaner (Techron) through a tank of gas?

It sounds like everything is in good working order from what you say.
I also have a BL WUR. I would try raising the steady cruise control pressure a little.
Not seeing your car or experiencing the problem and going from your description I'd try turning the allen head screw in the center of the large steel disc on the botton colckwise 1/4 turn. That will raise steady cruise and idle CP and lean it just a little.
If that doesn't help you can experiment more or put it back where it was and try something else.

Other people asked how i meant to clean the air flow meter housing and internal hardware. Remove it and clean it in parts cleaner and re lube the pivot bearings and contact points under the fuel head if things are dirty or gooey from age.

The height of the sensor plate at rest is also adjustable. It could be off a little.

Mark: Funny you mention those 2 tips. I knew I forgot some stuff the background section of my first post because I have done so much to get rid of this issue! I have completely removed the throttle body and sprayed out all passages, including removing the idle screw for cleaning. Nothing serious noticed and no change after reassembly. It has also occurred to me that if the throttle was being hung open for any reason, wouldnt that just give me a high idle and not a surge? Regardless though, I have also checked all linkages and verified the throttle plate does return to its rest position against its linkage stop, even while it surges. All return springs are tight and in place as well.

Ive also ran numerous bottles of chevron techron fuel injector and fuel system cleaner (not at the same time) as well as the tried and true "top engine cleaner" from GM. That stuff comes in a little bottle that you add to a bigger bottle of techron, then add to the fuel tank along with a fresh fill. It works great at mostly cleaning carbon buildup out of the combustion chambers, but does clen other areas/components as well. I have verified results with a 5 gas analyzer before (on other cars) and I swear by the stuff. As I type this, yet another bottle of techron fuel injector cleaner is mixed with the gas thats in the car from my last fill up.

J: I have tried warm cp's from 3.4 to 3.7 with no change. It runs best at 3.4 (albeit a little rich at cruise) due to it giving me the ideal afr just prior to the rpm delay at 4k rpm. If I raise it, the afr is just a bit on the lean side (IMO) prior to 4K...so 3.4 is where it looks best. Does the warm cp have an effect on idle (obviously to a certain extent)? I can adjust the afr at idle independently with the CO screw. If im misunderstanding this, please fill me in.

Height of the sensor plate is possible, but its never been touched and this surge did not occur with the old K27HFS, or the old 3LDZ prior to that. Very strange, but it could have fallen out of its adjustment. Again, I doubt, but its possible.

And yes Mark, its VERY strange how I can get it to stop every time I play with the pedal. Sometimes I have to play with the pedal a few times, and sometimes just once, but I can get it to stop fairly quickly. Let me tell you, Ive gotten good at it too! Its annoying as hell sitting at a light and having it surge! haha. I thought for sure that would tip someone off as to what it is. I guess not..

Yes, the 4mm allen head for warm CP adjustment on the bottom does affect idle and steady cruise AFR to a real small degree if you turn it only 1/4 turn at a time.
Brian had mine set at 4bar for steady cruise.
If you have the instruction manual he gives you with it I'm talking about figures 2A and 2B.
If you want to lower boost CP to get more fuel on boost after doing that then use the tool he gives you to draw out the steel disc on the bottom in figure 3A.

After doing all that you may have to do a fine adjustemnt on the cold start CP on the top of the WUR.

I have a flowtech IA modified fuel head that flows +20% under boost so my CP's are tuned around that fuel head and will be different than a stock fuel head.
I have CIS gauges and very rarely use them on my car. I adjusted the WUR and system pressure on the fuel head by experimenting alot, road testing, and a wideband AFR gauge.

4 bar would really help my cruise afr out a lot! But, a third gear pull at WOT would most definitely show a lean condition prior to the 4k rpm enrichment switch. Brian had mine preset at 3.8 when he knew I was running the HFS. I forwarded him a few dyno pulls with afr readings and he recommended lowering warm cp until I reached a safe level. 3.4-3.5 is where that ended up being with the HFS. I have it at 3.4 with the GT35.

The boost cp is fine. It dips nicely at 4k and does not lean out on its way to 6800 rpm (has aftermarket rod bolts), or at least it didnt with the HFS. My boost level has not changed so I have a feeling it will look very similar if and when I retest all the way to redline.

I also tune with an LM2 when its not on a dyno.

I have an rpm switch set at 5000rpm and boost line solenoid for the WUR and was using an HFS at 1 bar with the IA fuel head.
I never checked to see what the CP's are other than cold start.
I adjust and go by the way it runs and an AFR gauge till I like it.

7006 on the car now.

A little OT but what kind of cruise afr's are you seeing? Idle afr?

I'd like to see how they compare with mine, even though I know our set-ups are quite different.

Dont think you answered my exact question so let me try and be a bit clearer.

I totally understand that it will have a direct effect on the idle afr IF you dont touch the CO screw. However, I make adjustments with the CO screw after each warm CP adjustment. So, for example, what does it matter if the warm CP is set at 4 bar or 3 bar (nevermind cruise)? Does warm CP have an effect on idle recovery or something? I kind of perceived it to have little to no effect on idle (unless of course its something like 0 bar) when you can tune the idle afr to whatever you want.

I'm only suggesting you try what I said and see if it helps. I don't know if it will or not but there's a chance it might.

Adjusting the idle AFR by the CO screw has no direct effect on idle or cruise control pressure it is just reindexing the location or height of the control plunger in relation to the metering slits in the fuel head in relation to the position or height of the air flow meter sensor plate.
So adjusting the CO screw will have absolutely no effect on how hard control pressure pushes the sensor plate upwards against the force of air pushing down on it.

Adjusting the 4mm allen head on the bottom of the B.L. WUR for higher control pressure will affect control pressure at idle by pushing the control plunger downwards and the sensor plate upwards, higher than it was at idle and steady cruise so while it is for adjusting steady cruise warm AFR's it also affects the idle AFR.
Your car is running rich at idle so I would try a 1/4 turn clockwise on the 4mm allen head in the middle of the stainless steel disc on the bottom of the WUR. That will raise CP a little bit and push the airflow metering plate up with more pressure, raising it a hair higher.
You said if you let off the gas slowly your idle is steady and that makes me think the metering plate is settleing to higher position at idle when you do that. Raising control pressure will also make it raise to a higher position at idle so thats why I suggest adjusting it.

I have adjusted my WUR to have these AFR's with the IA modified fuel head when warmed up:
Around 14.5:1 at a steady 30-40mph cruise for decent gas mileage.
Around 13.9-14.1 at idle. Idle is smoothest around 13.5:1-14:1 in my car.

I can adjust it leaner easily with the CO screw but then idle lowers and becomes less smooth. Idle at 14.7:1 is not as smooth as 13.7:1 with 964 cams.

Boost AFR's depend on what rpm and what gear your in. They are far from perfect but CIS never will be and I'm not into spending/wasting any more money on frequency valves and controllers to try and make it better or flatter.

The modified flowtech IA fuel head and B.L. adjustable WUR were almost $1000 together and that plus the AFR gauge and rpm switch/vacuum solenoid and time spent adjusting things over and over are enough time and money spent on the AFR subject for me.

I don't know if that answers your questions but you can try raising warm steady cruise and idle control pressure a little at a time like 1/4 turn clockwise to start and if it doesn't work you can very easily return the adjustment to where it was in a few minutes if you have a small air cleaner on the car during the adjustable WUR tuning process so you don't have to remove the intercooler and factory air cleaner to get at the WUR every time.

When I was adjusting my WUR daily I didn't replace the 2 - 10mm nuts that hold it down everytime, I just slid it off the 2 studs without even removing the 2 fuel lines and tipped it sideways to fit a 4mm allen wrench in there to adjust warm steady cruise control pressure or AFR.

You have to remove it to tap in the stainless steel disc on the bottom with a brass drift and small hammer for lowering boost control pressure to get richer acceleration AFR's.

Ok, well as I said Ive tried warm cp's 3.4 to 3.7 with zero effect. I do appreciate the tip though, but Im not sure if the adjustments Ive made have proven it not to help? Perhaps, i should go above 3.7bar and see. Of course this means I wont be able to any hard accelerating due to the lean condition it will cause prior to the 4k rpm enrichment switchover.

I see you keep saying my idle is rich, which Im going to assume you think its a rich surge. Ok, but once I get the idle to settle, its 13.6 to 14.1:1, which to me, looks very good. If I lean it out (which Ive tried) to get rid of the surge, once I get it to settle, the idle is quite a bit leaner, sometimes in the high 16's:1! To me, thats not right, and not to mention the damn surge continues on the next drive cycle!! It does change the intensity and speed of the surge though. One thing is certain, so far it always returns no matter what adjustments are made, its truly makes very little sense. Due to the fact that nothing Ive touched thus far has seemed to cure it, Im thinking Im poking around in the wrong area(s) entirely (duh!), and the problem would have to be internal (such as fuel distributor) or god knows what else.

I appreciate your help so far as well as your afr details. My cruise afr is around the 13.5 or a tick lower. Its not the greatest for gas mileage thats for sure, but anything leaner and im not in a safe range under full load/WOT. For me, it looks like a trade off, and Id rather see cruise mpg's go down versus a $costly$ lean condition.

I will slowly raise warm cp again and maybe something different will happen, who knows.

[QUOTE=JFairman;4964824]

I have adjusted my WUR to have these AFR's with the IA modified fuel head when warmed up:
Around 14.5:1 at a steady 30-40mph cruise for decent gas mileage.
Around 13.9-14.1 at idle. Just about exactly where I have mine set. 14.2 steady cruise, 13.8 to 14.0 at idle. And I still have the stock fuel head and cams.

The modified flowtech IA fuel head and B.L. adjustable WUR were almost $1000 together and that plus the AFR gauge and rpm switch/vacuum solenoid and time spent adjusting things over and over are enough time and money spent on the AFR subject for me.QUOTE] Well said Jim! Before I started adding all the CIS "bandaids" and on-board AFR gauges, I felt better. Now, I've got too much information, forcing me to always seek the perfection that CIS will never deliver. Sometimes too much information is too much.

Mark, im jealous of your steady cruise afr. I know no 2 cars are alike, but just for reference, happen to know what your warm cp is set to? And do you have the rpm switch installed? If so, whats your switch set at?

Have you got any afr plots that I can view, or that you can describe to me? Im mainly interested in seeing a nice third gear WOT pull, as thats when I do most of my testing.

Warm cp at 3.75, enrichment cp at 2.5, idle CO% about 2.5%. RPM switch set with 4800 chip. 3rd gear WOT settles in at 12.0 most of the time, sometimes a touch into the high 11's (I should probably tweek the afr's down to the mid-11's on boost, but I'm not really too worried about 12.0 for short bursts). I don't have an afr plot, just watch the gauge with one eye while the other watches the boost, the tach, the speedo, and finally the road.

Real interesting set up you have there. I guess it REALLY goes to show how different each 930 can be. Man, if I try a 4800 chip, I'd be lean for quite a while before enrichment kicks in. Can you tell me what your afr is from 4000-4800rpm at WOT?

On a dyno pull for mine, I see peak torque occur at exactly 4k rpm.

Oops...correction, I'm running with a 4600 chip. It progressively lowers as the rpm's build and is around 12.4 well before 4600 rpms. Everything happens so quicky that it's hard to visually plot stuff while blasting down the road.

Sure would be nice to put her on a dyno some day, but my guess is the nearest one is over 100 miles away and I don't know of a tuner familiar with the 930 (other than myself) around here. I run the car, listen closely, feel how it's performing, watch the data stream, and tune accordingly. I think these cars are quite a bit more forgiving than we're often lead to believe, especially for a street driven car, but if I were a dedicated trackster running full-on boost for extended periods, I would want to entrust it to a dyno and professional tuner for safety sake.

I was seeing 12.6 to 12.7 prior to my 4k switchover at 3.75 cp and IMO thats a little bit too lean, especially with a faster spooling turbo and where the torque curve is. It did give me a good crusing afr though. So I lowered it and lowered it and ended up at 3.4 cp, and now Im at about 12.3 afr now before 4k. Cruise afrs are a bit down, but under WOT everything looks good. I have been doing a TON of searching on here and looking at dyno graphs that have afr plots. It seems lots of folks are delaying the enrichment well into the 4k rpm range (as you are) but all the afr's prior to that are in the 13's! Something to note though, on the dyno it was set at 3.7, and it sounded good and pulled good. IMO that goes to show you not everything can be felt or heard.

And yes, everything does happen quickly! I use an LM2 and thats where the record feature is real nice.

I also think you are true when saying that they are a bit more forgiving than we like to think. Its risky business though, as errors or mistakes on our part can be costly!

I think many are able to get away with a longer delay (4800-5000 rpm...and some even higher) before boost enrichment because the risk of detontation becomes more of an issue at the higher rpm echalons. Besides, you really don't want full boost enrichment giving you 10.0 AFR's at 3000 rpms just because you've got full boost and the WUR is doing it's thing early. Just robs you of power. Such is my understanding, anyway, of the logic behind it all.

So your AFR's may seem a little high on full boost (especially with the faster spooling turbos) but your rpm's haven't caught up yet. With my setup I could go with a higher rpm pill (and I did for awhile run with a 4800) because my turbo isn't really getting with the program until around 3800...and it takes only a second to get from 3800 to 4800 and the boost enrichment to begin.

Up top, im fine. 6800rpm and its at 11.7-8.

I guess you could say I tuned it around the peak torque curve, and thats because I had the luxury of knowing where it occurred. The dyno operator and Brian Leask were both in agreement about what should be done to correct my particular situation.

We all see what happens when people tear down their 930 engines here. Most of the time its not cool. I wonder how many are delaying for too long (creating lean conditions just prior) and what the consequences are. If its working for you though, cool. It may not hurt, other than a long drive, to see your power curve on a dyno.

I appreciate all of your input though Mark and I guess we'll have to see what I do to cure the surge.

In 2nd gear, just rodding the crap out of it (for me, that's just over 6 grand), I see about 11.5

I wish I could help with your weird surge problem. I had a surge at steady cruise 25 mph that drove me nuts, but just had to tweak the mixture screw on the fuel head. That was in the very early days way before I knew squat about these cars and just didn't have the mix right. You've got a lot of good input here, but also have pretty much ruled out everything. Try stuffing a gas soaked rag down the fuel tank and torching it when all else fails.

Just curious: Have you put a timing light on when it's doing the funky chicken? I wonder if your timing is dancing around appreciably. Could be an erradic vacuum retard signal getting to the dizzy...retarding, then advancing rythmically. Why, God only knows. Leaky diaphram in your advance/retard can attached to the dizzy? And I can't remember if you're running with all Lambda O2 emissions crap or not (O2 sensor, electrical solenoid and/or temperature sensitive valve to the vacuum lines to the dizzy, frequency valve that leans her out based on the sensor input, etc.). Major long shots....

At this point, Im all about long shots! I have not put a light on it to see what the timing is doing. If i had to guess though, it would probably be moving just like the afr does when its surging. I will confirm that though this weekend. I had the entire dizzy apart 6 months ago for a general cleaning and lube. At that time, I made sure the diaphram held vacuum, which it did. I will also re-confirm. Car ran fine afterwards.

No O2, but the dizzy does have the thermo valve and the other switch still inline with the vacuum lines. I believe they are working correctly. The idle will kick down after a minute or so during cold starts. I believe thats one of the functions of either one, or both, of those dizzy devices? Can I simply leave those items out of the loop for testing purposes? I think the answer is yes but just double checking. Frequency valve still installed. How do you check its function?

I also want to say that I dont mean to or want it to look like I'm shooting people's suggestions down (in a rude way) because when I say Ive checked everything, Im not kidding! The amount of research and testing Ive been through is no joke.

[QUOTE=DailyDriven'88;4968462]No O2, but the dizzy does have the thermo valve and the other switch still inline with the vacuum lines. I believe they are working correctly. The idle will kick down after a minute or so during cold starts. I believe thats one of the functions of either one, or both, of those dizzy devices? Can I simply leave those items out of the loop for testing purposes? I think the answer is yes but just double checking. Frequency valve still installed. How do you check its function? [QUOTE]

You can just route arouind those solenoids and valves, and you would primarily just lose the additional advance for the first minute of cold start. Instead, the vacuum retard would be there right from the start instead of being delayed. To be honest, I suprised the solenoid even works since your O2 sensor is disconnected, but it's obviously an isolated function controlled by the same box under the seat that controls all the other Lambda functions. I was just wondering if the solenoid was being spassmic; stopping retard/allowing retard either because it's triggering when it shouldn't be or it's internal mechanisms are beginning to fail (i.e. leak). If you were to unplug and then plug back in your retard vacuum line at the dizzy once every half second, would you get the same weird idle?

Testing the frequency valve....well, all you can really do is listen to it buzz (engine off, key on, force the pumps to run and you'll hear it buzz away). Unplug the connection, plug it back in and listen to it. If it failes, you'll have problems with very lean conditions. Can't run without it (at least not without adjusting all 6 fuel plungers in the fuel head to compensate).

This is a diagnostic mystery. I just seems to me that you're chasing a vacuum issue somewhere.

Roger that. I will bypass them and see. Your theory about the dizzy retard sounds like it could happen.

Doubt the frq. valve is bad then, since I dont have 'very lean' conditions.

I asked this question on the first page, but didnt get a response. An opinion, or possibly fact, that idle surge is caused by a rich condition. A vacuum leak creates a lean condition at idle correct? Its unmetered air, which equals less fuel. How does that hold up to the rich surge theory?

"An opinion, or possibly fact, that idle surge is caused by a rich condition. A vacuum leak creates a lean condition at idle correct? Its unmetered air, which equals less fuel. How does that hold up to the rich surge theory?"

A rich idle mixture in a fuel injected car will always cause the rpms to oscillate up and down and thats a fact. I used to work on German cars for a living and I've seen this with CIS or K-jetronic, L-jetronic, Motronic, and the kugelfisher mechanical fuel injection used on the old BMW 2002 tii's
I have never experienced this with a carburator running rich at idle though.

The answer to the other question is more complicated.
All air leaks in a turbo cars intake system are often called vacuum leaks even though some are actually air pressure leaks because it's easier to group them all together in conversation without getting overly techanical and people that are familiar and experienced with turbo cars understand the differences.

An air leak below the throttle butterfly will be a vacuum leak of unmetered air at all times and cause a lean situation unless the turbo is boosting and the throttle is open far enough to let in more boosted air pressure than the intake ports and cylinders can swallow, then it will cause a rich situation because metered air is leaking out to atmosphere while metered fuel is being injected into the intake ports.

An air leak after the turbo and before the throttle butterfly, or blow off valve will be a pressure leak at all times other than when you first snap the throttle open before the turbo spools up.
The turbo is making pressure in the intake before the throttle body at idle and steady cruise, it's just low enough to not show on the boost gauge.

This is metered air so if any is leaking out between the turbo and the throttle body it will cause a rich mixture.

Have you tried lowering boost control pressure with your Brian Leask adjustable warmup/control pressure regulator yet?

Jim,
Great job describing how vaccum and boost leaks differ in their affect to mixtures in boosted applications. That's always a tough one to internalize.

But you lost me in your final comment re: lowering the boost control pressure. Are you referring to that as a possible cause of rich idle?
It's been my understanding (fact or fiction?) that the WUR boost enrichment is fully in by around .3 bar or so. Correct? So even though at idle where there isn't enough boost to register on the gauge, we will still see some level of enrichment occuring via the boost signal at the WUR? And if you were to lower the boost CP at the WUR, then affectively you would get even more fuel vs. air at these very low idle boost conditions due to the lowered fuel pressure resistance at the control arm? So, if a surging idle is the result of being too rich as a result of the WUR's boost circuit, wouldn't he want to try increasing the boost CP to lean out the mix?

I must be missing something in the translation. You da man with all that German- Beemer experience.

I said that because I asked him to raise steady warm cruise CP a few days ago (which would also raise idle CP a little) to see if it would push the metering plate up a little higher leaning out the idle mixture a hair and see if that would stop the rich mixture rpm oscillation at idle.

He says he can't do that because it will lean out his boost CP at the same time. Fine, that is correct to a degree, but that is why I suggested lowering the seperate boost CP adjustment to compsnsate for raising steady cruise/idle CP.

All 4 seperate spring pressure adjustments on the BL adjustable WUR affect each other and once you get one set right you have to go back to the others and reset them too until you find a balance that works on your car and it's state of tune.

I've readjusted my B.L. adjustable WUR around 40-50 times trying to tune around 2 different Flowtech/IA modified +20% fuel heads until I got things as good and consistant as I can get it.
I don't think there's many people out there other than Brian Leask that have spent as much time adjusting his WUR's as I have and know the results as well as I do. It takes an incredible amount of time to tune around a modified fuel head from the beginning.
Now I know where to start with one if you're using it on the street and you want to get decent gas mileage still.

The boost CP adjustment is the approximately 15mm round stainless steel interference fit disc on the bottom of the WUR. It is setting spring tension internally.
The 4mm allen head adjustment in the middle of this disc is the warm steady cruise/ CP adjustment.
These 2 seperate spring tension adjustments are very adjustable and sensitive and can make big differences in the CP's and AFR's under boost and or steady cruise.
If you have the rpm switch and vacuum solenoid on the MAP line to the WUR you don't even have to mess with the threshold adjustment because the boost clamp overrides it and is much more effective.

When you get all the other settings right, you go back and reset the cold start CP a little and you're done.

I have also experienced on some electronic FI cars where a vacuum leak will cause a surge/oscillation at idle and if you combine that info with a rich condition on a carb'd engine not causing the issue, that just shows me just how different many of the systems out there respond to different situations. Thanks for the clarification.

You got me thinking about an air leak after the turbo but before the throttle plate. I have new O rings throughout but what if the BOV isnt sealing tightly? I put in new seals about 6 months ago but I did happen to hear a ticking noise from that area the other day (not while it was surging). It sounded like the recirc valve spring inside rattling. I havent heard it since. I may throw new seals in there again for the hell of it.

Jim, have I been mis-reading this whole time? Are you suggesting raising warm cp or boost cp? I thought warm cp. The car does have the rpm switch so how would boost cp have any effect on idle? I can see how it would be possible if I didnt have the switch.

Mark: I did bypass the 2 switches inline with the dizzy vacuum lines and no difference other than a lower and rougher idle during cold start. I will probably hook them back up.

Now I think Im more confused, haha. If I raise warm CP, it will create a condition that I believe is too lean prior to my 4k rpm switch. Are you saying I can alter that lean condition by adjusting boost cp even though Im before my 4k switch?

If you have a Brian Leask adjustable WUR like you said you do....
Most likely yes, but all cars are a little different so again I'm just suggesting things that have worked for me on my car..

But I guess you havn't tried the warm steady cruise +CP adjustment I suggested so why doubt or question the boost -CP adjustment I suggested twice now to compensate for it if you did.

I doubt and or question it because Brian Leask himself suggested the warm cp adjustment only, nothing else, since the rest of the afr graph looked good.

I can and will try your suggestion this weekend. I did the dizzy switch bypass because it took me all of 2 minutes to do. Your suggestion takes a little bit longer, even if my WUR still isnt bolted down. To be honest, I missed the - boost cp suggestion until Mark asked about it. I assumed you just made a typo.