Turbo Swap : And then there were none....

[RarlyL8]

Stole a few hours this weekend to work on the P-car.

Quick recap of events:
Transplanting a '78 930/63 engine into a '78 SC.
No smog equipment, euro exhaust, US/ROW distributor.
Idle is high (2200 - 2400RPM)

After many battles with the timing and vacuum leaks I finally threw up my hands last week and decided to remove the entire CIS and inspect every square inch of it.
I found nothing remarkable. The system was carefully inspected and reassembled. I removed the vac valve between the pop-off valve and the intake, plugged the lines.

These are the only components left on the CIS:
Air meter and fuel head (obviously)
WUR
Throttle Bypass Valve

THAT'S IT!!

After refitting the CIS and the pop-off valve the intercooler was put on and the engine started. It kicked on the second hit and slowly rose to ~ 2000 RPM. After about 2 minutes it kicked down to 1700 RPM and stayed there.

I checked the timing - it was right on TDC @ 1700 RPM. Well I figured this is as good as I'm gonna get it for now, time to move on to the fuel mixture. The original configuration for this engine was California smog so I figured it would be running a bit lean with stock settings and euro exhaust. Oh it was alright, the gas tester blipped out a 0.2% CO @ 1700 RPM. After many adjustments I finally got it to 2.7-2.8%, good enough for now. I took the intercooler off (again) and replaced the stock air cleaner. Put the intercooler back on and fired 'er up.
1500 RPM rock steady.

Looks like we're (very slowly) getting somewhere, but I'm not sure where. Still need to shave 500RPMs off, and the idle screw is still fully closed!

I got brave and decided to take a spin around the block - you will remember last time I had no brakes and about ***** myself. Well this time the brakes were back. The car runs strong and wants to rev, but has that pesky high idle.

There are only two CIS components left. I removed the WUR a few weeks ago and found no difference. So now I'm staring at the Throttle Bypass Valve (the phalic symbol looking thingy that sits just right of the WUR). This valve connects the intake to the intercooler and seems like a dandy candidate for a leak.

Any thoughts?

[beepbeep]

Just one question...

Is there any special reason you don't want to adjust timing @ 4000 RPM as stated in factory manual?

Also, engine cannot idle if it cannot draw air. So obviously, air is finding it's way into engine for some reason. If idle-screw is fully closed than there are only two possibilities:

1. You have vacuum leak somewhere
2. Fallos-thingie is leaking air.

(If you open the "fallos" you'll find small disc that rotates when you apply current. If it's stuck or busted you will have vacuum leak.)

Good luck!

[dean]

[QUOTE]Originally posted by beepbeep
[B]Just one question...

Is there any special reason you don't adjust timing @ 4000 RPM as stated in manual?

[QUOTE]

Because he is very stubborn

[dean]

I also think that you must have a vacume leak. You could use water from a garden sprayer to spray the motor. That way you wouldn't have to worry about flooding the motor with carb cleaner

[juan ruiz]

Don't feel bad Im in TIMING Torture Zone too!

[john walker's workshop]

clamp the hose between the intercooler and the air regulator and see if the idle slows. also check for power at the air regulator plug.

[RarlyL8]

There is a reason why I don't check the timing @ 4000RPM.
I have no help.
There is no one to hold the throttle at that speed. The engine revs so freely and quickly that I cannot prop the loud peddle just right. You can't even THINK about using the throttle lincage with all the crap in the way.
Anywho, that isn't the real problem. I've got a vacuum leak somewhere.

John - what air regulator are you refering to? The throttle bypass valve? How does this valve work? The Bosche manual does not even mension this valve. What is the action taken by the device when electricity is applied, and when is it applied?

My next move, as sugested in the original post, is to remove or plug this throttle bypass valve. There just ain't much left of this system to check.

[beepbeep]

As far as i remember, there should be some sort of solenoid that operates shutter-disc. When current is applied, disc will turn and open the gap, allowing air to go trough. I believe it's operated by thermo-switch of some sort and is open until engine heats up.

Jocke had problems with high idle on his 930 and found out it was just bad connector on this air-regulator valve.

After that, there is nothing else to check but cracks in the fenolic intake-spacers or intake itself, considering that you closed/dismounted everything else :-).

Cheers!

P.S.
I recomend finding help and adjusting ignition timing @ 4000 RPM first, as it isn't affected by vacuum leak but it does affect idle speed. You can always tie a string underneath to throttle actuator and bring it to 4000RPM yourself, or lodge something between the seat and accelerator pedal.

[beepbeep]

P.S. This should be the evil regulator:

[dean]

I didn't know that you can't get at the linkage. That makes it much harder to time by yourself. Get the wifey to help.
That valve should be bypassed to test it. How about any other fittings on the intake? Disconnect and plug all the things on the intake. Like the brake booster line, the wastegate line, etc and see if the idle is good.

[RarlyL8]

Yes Roadrunner, that is the evil throttle bypass valve.

Blown, I replaced 4 out of 6 injection blocks that had cracks in them. The wife is not allowed in the garage unsupervised. It would be her greatest delight to fire up the 911 and jam the throttle down 'till she blows. That's right, she's not too happy about this situation.

Well I talked the missus into visiting the in-laws for a bit. As soon I she left I bolted out to the garage to started in on this valve. The first thing done was to start the car and let it wasm for a couple of minutes. Idle speed ~1800 RPM. Before it could get too warm and kick down I shut 'er off. Removed the hose between the throttle bypass valve and the intercooler and plugged both ends. Hit the key and gueeeeeees what -
it idled at 1000 RPM - cold. That dirty rotten SOB of a valve. The only one I didn't check and the last one left standing.

Now a few questions. This valve bridges a huge vacuum line between the rear of the throttle plate area and the intercooler (hence the name). It is electrically inervated. Where is it getting its power? There are no switches left on this system, I have removed them all. To my knowledge none were connected to this switch.

Beep - you say that when elecricity is applied the valve opens. Does this mean if I simply unplug it the valve will stay shut? That would sure be an easy fix for now. I'll give that a try when I check it for power.

Thanks all for your help. My brain has really turned to mush on this one. Fresh eyes are a big help.

[dean]

That valve is called the Aux air valve. It is for fast cold idle. You can look in your factory manual and it will tell you about it. I can't quite remember but there is supposed to be a resistance value across the coil of the valve. Maybe 300 ohms or something. You can bypass the valve for now if you want to drive your car. My 75 ROW doesn't even have one. So on cold mornings I have to rev the motor myself.

Isn't it always the last thing that you check.

[Mike the mechanic]

Rarly, I don't have much experience with 930's but I have much experience with CIS powered Volkswagens. The Auxilary air regulator should be the same in both. The way it works is, the disc is open, allowing the air to bypass the throttle plate hence, allowing the engine to idle high. The regulator receives battery voltage when the engine is running, heating the element and allowin it to close incrementally as the engine heats up. The way to check these valves is to let the engine warm up, and clamp one of the hoses with a needle nose. If the idle drops, then the valve is either sticking or not recieving its signal voltage or ground.
As i said, I am not sure that the Aux air regulator is the same as the VW units.

Mike
86 Carrera (soon tt)

[beepbeep]

I think i remember how it works now...

There should be a electrical heater inside "fallos" that slowly heats up bi-metal spring. After it get's hot, spring (with two metals with different thermal characteristics) will twist the disc, shutting off the passage of air.

With other words: this thing is open by default until it heats up, so unplugging 12V probably won't shut it down. Measure heaters resistance with ohm-meter and see if it's OK. Otherwise, plug this hose for good.

Also: 1000RPM is still too high considering you shut all other passages down. Your engine should bog down/idle very low when you plugged this valve but is still getting air from somewhere...find that leak!

Good luck!

[TurboRuf]

>it idled at 1000 RPM - cold. That dirty rotten SOB of a valve. The >only one I didn't check and the last one left standing.

Same part that was causing my cold start problems....Grrrr. Congratulations on your discovery! Keep us posted on how everything turns out.

[RarlyL8]

If you fellas remember waaaaaaaaay back when this nightmare first started, the aux. air valve was the FIRST thing removed.

Now I see what is going on. This rediculous, piled on, cobbled together example of 1978 smog control genious has no less then THREE devices that act in the same manner as an auxilary air valve. The unit in question is called a (1) "Throttle bypass valve" in the 930 factory manual. There is another large round vac pot that shares the same large vacuum line, the 930 manual calls this unit the (2) "Auxilary Air Valve". The third unit is located under the pop-off valve and is called a (3) "Vac Control Module".
The (2) "Auxlilary Air Valve" is the one I removed first.
When I went back to the Bosch manual last night I turned to the chapter titled "Auxilary Air Device". There in a nice black and white drawing was this bastard part that Porsche refered to as the Throttle Bypas Valve. I remember reading the chapter long ago but the picture didn't strike me as remarkable.

SO - it looks like they pull a name out of ass for this stuff. Thanks a bunch. I'm gonna yank this final piece of crap out and cap it off as well. Looks like all you need to run a CIS motor is a fuel head, air flow plate sensor, and a WUR.

Beep, you think I still have a leak. The engine was cold when I shut down "Auxilary Air Device #1". I did that purposefully so the WUR would still be active and keep the engine from dying. For the first time I actually smelled fuel from the tailpipe - an indication that the WUR was working without all the extra air. Next time I get a change to work on the car I should have to open the idle screw to keep the engine from dying when warm. How many turns out does a "normal" engine use?

The plan has been to eliminate all this crap and install a hand throttle like I had in my MFI 2.4T. Nice and simple.

[Superman]

Don't know much about turbos but have have advice anyway. Listen carefully to JW and do exactly what he suggests. When I've failed to do that, it has cost me...... He knows the quick way to do stuff and he's got turbo stuff everywhere in his shop. So if it were me, I would:

clamp the hose between the intercooler and the air regulator and see if the idle slows. also check for power at the air regulator plug.

[RarlyL8]

I think the "air regulator" that JW is refering to is the auxilary air valve #1 / throttle bypass valve that I blocked off.

See the problem with the name game?