Fast cold idle 930 sorted
 

Hello to the forum and hopefully someone can help me with this inquiry.
I have a 1979 930 which has a cold idle speed problem. When the car is first started cold it fires on 2,3,4 and finally all 6 cyliders before settling in to an idle speed of around 2000rpm. Once the car is driven to warm the idle comes down to a respectable 7-800rpm. I could almost live with this apart from the fact that if I leave the car for more than 10 minutes anywhere it's back to stage one again even after it has been driven for some time and the car is warm. To add to this if the weather is above about 22 deg. C (72 deg. F) the problem is less severe but still far from right. As well as this, now when full boost comes on the engine shuts off completely and the ignition needs to be turned off and the engine re-started. This can be done immediately and the engine will start again no problem. When I first had the engine re-built about 4k miles ago there was a problem with a blocked wastegate atmosphere pipe which had a similar initial effect after creating an overboost, but the engine fired again as soon as the revs droped and boost was lost but this problem is different again.
Any suggestions re these two problems would be great. Thanks Konrad.

For the second problem, could it be a stuck relay? Have you tried a replacement relay to the overboost one in the engine compartment?

Much of the first problem is somewhat normal, minus the fact that it doesn't fire on all cylinders, and the idle speed sounds a little high. The car is made to idle high after a start, even after a short cooling period.

Interesting. I'm pretty sure I remember John Walker's Workshop posting on a similar thread on the 911 forum and remarking that they fitted SC AAV's back in the day to reduce the "obnoxiously high warm idle".

A high idle is probably better when it's stone-cold though - at least you're getting decent oil flow if you don't drive away immediately like the handbook advises you to do...

Thanks for your replies - I've just replaced the vacuum hoses & clips to the warm up regulator just in case but no change. Also found a clip missing from the intercooler to wastegate hose which I replaced although after driving round the block with the idle still at 2000-2200rpm I didn't persevere to see if this was the problem behind the shut off under boost. I'll check the AAV hoses tomorrow - Thanks Guys

Check your IC o-rings too.

Thanks again to everyone for the ideas and links.
After removing the AAV and testing it in the oven for about 10 minutes to see that it was working, I reinstalled it. And then as we say here "Well bugger me" the car started cleanly and settled into a stone cold idle of about 1400rpm. Not quite understanding what had actually changed (and yes I waited for it to cool down first) I decided to tap the body of the AAV the a screw driver handle and as I did the revs came down with each tap to settle at about 11-1200rpm. While out of the car I could see that the inside of the unit was a little dirty but they're obviously designed not be opened. Any clues on cleaning? Alas the shut down under what is very early boost still exists but for today I'm not complaining. K

what is an AAV?

Auxiliary Air Valve..

ah, tanks...me no big fan of TLA's (three letter acronyms!!!!!)....i'm curious as i have a high idle initially on cold start, initial leap to 3K then back down to 2K which will dissapate after about 20mins or of driving. however if i stop and start within the 20mins, it's back to 2K rpms for a few....perhaps i should check my AAV make sure it's clean.

best, Paul.