She Liiiives!!

[PrimeMvr]

I woke sleeping beauty from her 4 month winter slumber tonight. Thanks to great storage tips from Grady and others, it fired after two seconds of cranking with zero smoke. I bought this 930 right before the snow came, so I have very little experience with the engine actually running. A few questions that search hasn't answered.

1. I had to lightly hold the throttle open to get it to idle. After five minutes, it held a slightly wobbly 700 rpm idle. My AFR gauge is on backorder, but I know it's very rich just from the exhaust smell and tuning discussions with the PO. Is that enough to cause the idle issue? B&B headers and no smog gear.

2. Just to see if the K&N might need cleaning, I popped it off while running. The idle did not change at all. The air box was full of a thick vapor. Normal?

The idle issue existed before I put her away, but over the winter I cleaned all the plugs (black/sooty, but not fouled) and reconnected the NBO2 sensor. I thought that might be the issue, maybe it's dead I suppose, have to check that out this weekend. The engine is very strong mid-to-high revs, but the low end is sluggish.

The good news is that off-idle its smooth, there are no unusual noises and again, no smoke. After reading so many posts about how oil can pool in the chambers I purposely waited until dark for the first start up, just in case!

I'm not a car rookie, but this is my first P-car. I've been reading this board nearly every day and love it. I'm learning, but every time I get in the engine bay, it's an excercise of "I wonder what that does..." I have a factory workshop manual and Wayne's 101 book, but both assume you have some knowledge of Porsche engines and leave out a lot of the basics. Any suggestions for education and my two issues above are greatly appreciated.

Thanks,
Steve

[mark houghton]

Could be that your O2 sensor is kaput (that's the Motherland language for toast), thus throwing off your tune (mixture) at idle. Could be that it's working just fine and your plugs are worn out. Could be that you can fix the idle simply by adjusting the mixture screw out to lean it (counterclockwise) just a smidgen (as in a couple degrees rotation...it doesn't take much to have an effect). Then re-adjust your idle speed screw.

Could also be that your AAR is stuck closed and won't allow high idle when she's cold (try this: fire her up cold, get it to idle wherever she'll idle at, then pinch the hose to the AAR). If the idle doesn't drop, then the valve is stuck closed and not allowing any air in and thus not elevating the idle.

Those are the first areas I would look at. If you know anyone that has a tail pipe emissions sniffer to give you a read on the CO%, that'll give you some hints on where to start.

[pdx930]

One of the positive side of our lambda equipped CIS cars is that you can tweak the idle mixture by looking at the duty cycle of the frequency valve. Stick a dwell meter in the test port and adjust until the duty cycle is at about 50%. If your O2 sensor is working, you should see the duty cycle fluctuate about 5-10% around 50% once you have it tweaked in.

[mark houghton]

Originally Posted by pdx930

One of the positive side of our lambda equipped CIS cars is that you can tweak the idle mixture by looking at the duty cycle of the frequency valve. Stick a dwell meter in the test port and adjust until the duty cycle is at about 50%. If your O2 sensor is working, you should see the duty cycle fluctuate about 5-10% around 50% once you have it tweaked in.

So true. And another beauty is that these cars run just fine without the lambda by tuning open-loop with the sensor disconnected and the duty cycle fixed at it's default. Unless, of course, you're stuck with mandated emissions testing such as required in the Portland area. I can remember many many moons ago when living in Alhoa, waiting in line at the local DEQ test station in my old MGB, hoping and praying it would pass.

[PrimeMvr]

Thanks guys! Those sound like logical possibilities that I'll try out this weekend, or maybe this afternoon if I can manage to play hooky from work

I don't want to mess with the mixture until I get my AFR gauge installed. The PO was clear that it was tuned on the dyno to keep it rich on boost (354 whp) and I think the low end is suffering greatly because of it. I need to read some more to figure out how to get the best at both ends.

This is going to be a fun learning curve. My past cars have been old and carbureted, or new luxury cars completely computerized. The 930 is an interesting blend of computer and good 'ol vacuum control. Fun stuff!

[mark houghton]

Well then, assuming the car is in good tune left from the PO, then just turn up the idle a bit with the idle adjusting screw. Shoot for 950; 700 is a bit low for proper oil scavenging.

Tell us about what - if any - modifications have been made to support the HP claims. Also, does the car have an adjustable WUR? Yes, you can get a little top end enrichment benefit by setting the idle really rich, but in reality the benefit is not that great and doesn't do too much more than cause a crappy idle. To really fine tune the top end under boost requires a means to adjust it in that range (ie, adjustable WUR or something similar).

[PrimeMvr]

I'm still piecing the modifications together. I have the dyno sheets from last summer and know and trust the PO. However, the provable update history is sporadic.

The PPO (prev prev owner) did all of the updates, and he told me that it was rebuilt with 98mm pistons, ARP bolts, 964 cams, K29 turbo, Powerhaus intercooler. Some of this I can prove with invoices, some is just on faith. I plan on keeping the car for a long time, so at some point I'll have the engine apart and be able to document it better. No need for that just yet as the rebuild was 7k miles ago.

I've not dug under the IC or air box to see what components may have been changed out there. I don't believe there is an adjustable WUR. More research to come...

I can tell you that on the highway the engine is super smooth and power comes on like a sledgehammer at 3500 RPM under WOT. In 1st and 2nd it's a blur from there to redline. But off the line to 3k is almost embarrassing unless I rev and slip/drop the clutch, which is not my style. I bought this car to point and squirt on twisty country roads, not to drag race. It does the first part well, now I just need to clean up the "around town" behavior.

I will definitely twist the idle up a bit, but with my foot holding it at 1k, it still felt a bit rough. I'm going to get it out for an Italian tune-up tonight, but the Bosch plugs were clean and < 2k miles on them when I started it, so I'm not confident that will help.

Any guidance on a good engine tuning (rather than rebuilding) book for the 930?

[mark houghton]

"Italian Tuneup"....I like that! Does that mean seat of the pants tuning with reckless abandon down a long country road in the middle of the night?

Books...I can tell you're a book man such as myself. Information starved, the best place to start. See our hosts selections here: PelicanParts.com - Porsche Catalog > Pelican Parts Bookstore > Porsche Technical Books & Manuals

I would recommend Bruce Andersons 911 Performance book, the Bently complete 911 manual, and the Bosche fuel injection book to really understand CIS. What you won't find is a tuning book specifically for the 930...you have to grab bits and pieces of knowledge from all sources, and this forum in particular, to build your learning curve.

Sounds like your 930 is/was well put together and there are reasons for it being tuned the way it is. As far as off-line performance, forget it. These are low compression engines, not worth a crap until things start to build. You can help that a bit with free flowing intake and exhaust, and advanced ignition timing and the controls to remove that advance as boost builds, but otherwise expect mediocre performance off the line.

Oh....and run a bottle of Techron injector cleaner through it. Good stuff, to make sure all is clean in the fuel distributor and injectors.

[PrimeMvr]

Mark, you're slowly becoming my best friend I'm taking the rest of the afternoon off for a short drive, oil change, long drive. I'll pick up some Techron while I'm out.

First nice, dry day for four months. Not going to waste it!

[s_morrison57]

I had the same low power till about 3K and I put on a RarelyL8 exhaust (still waiting for the proper heat boxes before I spring for the headers) and it really transformed my car, sounds better and the turbo comes on smoother and earlier and at lower rpm it is way more responsive. For me it was probably the best bolt on part that I've ever bought, new to the P-car world but this pipe really made a difference.
Finn

[PrimeMvr]

Hey guys, here's an update.

I adjusted the idle screw. Had to back it out almost all the way to get to 900 rpm when warm. When cold it still stumbels around 6-700. I did the pinch test on the AAR and sure enough, the idle didn't change a bit. It looks like I may have found the culprit for the cold idle.

I spent most of the weekend tracking down an electrical gremlin, so I didn't have a chance to mess with the AAR.

Once warm, she felt pretty good on the road over 2000 rpm, but there are some slight hessitations through the upper rev range. I definitely have some mixture issues that I'm going to address after getting the AAR working and installing an AFR gauge that's due in on Friday. Going to replace the diz cap and plug wires also, plugs are near-new.

In the "crap, that needs to be fixed too" category, I found a sliced CV boot while changing the oil. Peeked inside and the grease is still thick and clean so hopefully it will just be a boot replacement.

Thanks again for your guidance. Steve

[PrimeMvr]

No I didn't abandon this thread, it's just taken longer than I expected to sort this out. I replaced the dist cap/rotor, plug wires, cv boot and installed an AFR gauge.

Tonight I started it up and the idle was still very rough and AFR was 9.2. Here's where it gets interesting. The pinch test on the AAR had no effect, so I pulled the hose between the IC and AAR and the AFR went to 12.7 and the idle smoothed right out.

Plug the hole to the AAR and it stalls. Not much change if the IC hole is plugged. There is good vacuum at both the AAR and IC hole. This leads me to the theory that there is a battle for air flow in the hose that feeds the AAR and nothing is flowing through it when it's connected to the IC.

Now what? I'm stumped on where to go from there. I assume the air should be able to flow freely from the IC through the AAR or the AAR would be pointless. Too much air restriction on the cold side of the turbo? I've read a ton of "rough idle" threads but none address this type of issue.

After 4 minutes of idling with the hose off, the AFR ran up over 17 and the engine stalled. I assume that was the engine temp telling the WUR to change fuel flow? At this point, with the hose reconnected it idled a little rough, but better.

After a drive the idle is smooth and stuck at 900rpm.

Thanks guys. Steve

[e170drvr]

What is your afr at idle when fully warmed? Is the o2 sensor still being used? If not try leaning the idle mixture to 13.4 afr which equates to 3% co and is the happy spot for most 930s. Be careful that you are not too lean at upper rpm. If you are lean up top, but good everwhere else you may be a good candidate for an adjustable wur. Rarlyl8 or Brian Leask can help you with all of this.

[mark houghton]

Had to read your post a couple times. So, you pulled the hose between the IC and the AAR and the AFR's went up. But of course, you at that point were drawing air into that IC hole that used to be connected to the hose going to the AAR. But if you now plug that open end hose to the AAR, the car dies, which says that the AAR is drawing air through it to support a higher idle. That air is going post-throttle body, whereas the extra air from the open hole in the IC is going pre-throttle body. At idle, the larger impact of the two would be air injected post-TB, which you proved by plugging the hose to the AAR and the car stalled. And you have good vacuum at the AAR, so air is being pulled through it.

My guess is that the AAR is working as inteneded (did you ever pull it off, or look inside the hole to see if it's open or closed when cold? Should be open). Or put it in the refrigerator, cool it down, see how much it opens.

9.2 AFR at cold start is a bit low, but I think mine starts out at around 10.0 and within the first maybe 45 seconds moves up to high 11's, and couple minutes later up to high 13's as the electrical element in the WUR heats it up.

e170drvr has some good advice. Lean that pig out a little bit (like a degree rotation on the mixture control thingy....counterclockwise). And if you are running with the O2 sensor, it could be FUBAR. One way to find out would be to unplug it and look for any change in idle. And yes, what is the AFR at fully warmed idle? And do you have acess to the fuel pressure gauge setup for checking cold and warm control pressures and system pressure at the WUR. It's a must have diagnostic tool.

I feel there is nothing more wrong other than it being out of tune. Verify the AAR is working, and if you're not sure about the O2 sensor then unplug the damn thing and tune around it (see what your AFR's are doing at fully warm idle and adjust for 13.5 to 14.5...let your ear tell you how she sounds).

[PrimeMvr]

O2 sensor is disconnected.

I'm still wondering why the AAR appears to not suck air through when it's connected to the IC, but does when the hose is off. It seems like there is more vacuum in the IC (Powerhaus) than in the AAR path, so air doesn't flow when the hose is on. The valve is definitely open.

Is this the fuel pressure tester that you would suggest? Pelican Parts - Product Information: TOL-TA33865

Bosch CIS book on the way also.

I plan on a good drive and data logging session tonight to look at the hot AFR curve better. Last night was just around the block to make sure everything was hooked back up. I'll tweak the mixture once I have better data and see if that solves it.

[e170drvr]

Prime, sounds to me like the aar is working as it should remember the aar when cold just opens slightly to raise the idle for cold starts we aren't talking a lot of flow going through there. My money is on you having a pig rich condition across the board, get an afr meter on that to confirm. Also the p.o. As you stated tuned it rich for the installed mods so the idle and off boost may be suffering. Some afr data will likely shed some light on this and we can go from there.

[e170drvr]

Looks like you are looking at fuel testers, that is another good move. If you plan on keeping the car for awhile the tester is an important tool to have.

[PrimeMvr]

e170, I feel like slapping myself for belaboring this, so you can slap me if you want, but....

While I agree that I need to spend some time on the overall fuel delivery, doesn't it seem odd that when cold and I pull the hose between the IC and AAR, the mixture goes to 12.7 (indicating good flow through the AAR) but attached to the IC it's 9.2? My inexperienced, but intuitive, mind tells me "air isn't passing from IC to AAR and into the manifold". This seems confirmed by pinching the hose when attached and there is no change in AFR or engine behavior.

Thanks for your patience with me as I weed through the CIS forest.

Steve

[e170drvr]

Well if you pull the ic to aar hose you are introducing a whole bunch of unmetered air, and I would expect the afr to lean out.

[mark houghton]

Originally Posted by e170drvr

Well if you pull the ic to aar hose you are introducing a whole bunch of unmetered air, and I would expect the afr to lean out.

Yep. You just opened up a 1/2" hole to the air intake by pulling the hose off the IC, sucking additional air into the IC beyond that which has already been metered. Up goes the AFR's.
Since the AAR injects air post-throttle body, there will be more vacuum than the IC side of the TB....so air will automatically flow from the IC to the AAR through the hose due to the pressure differential. But the air being used to feed the AAR is the same air that the engine will ultimately use and has been balanced with the fuel delivery as it initially deflected the fuel control arm. But by injecting some of it after the TB through the small opening in the AAR, it causes enough leaning to raise the idle.
Man, I know what I'm trying to say but it's hard to convey. Maybe another glass of Cabernet will help....