About a week ago my idle went crazy. The warm up is at 3500 RPM then drops to 2200 after that. I tried adjusting the idle screw. It had no effect. Any ideas as to the problem. I'm fairly new to Porsche mechanics. BTW, I have a 72 914.

Thanks,
Doug

classic symptom of the Auxilary Air Regulator (AAR) failing open - or the air line leading to it cracking or just plain breaking off. sometimes the wire that powers the heater gets wonky too - check it carefully - that circuit powers the fuel pump too.

other vacuum leaks can cause this but most are too small to have this kind of effect. but where there's one, there are usually others, so check 'em all.

the idle screw on the control box affects IDLE MIXTURE only. it does not work off idle, and it does not control speed - except to the extent that bad mixture will adversely affect speed...

good luck - and welcome !

Sounds like a vacuum leak. Pull the hose off that connects the AAR to the cold start injector. It should increase the idle. plug end of hose with finger. If idle goes to normal, then the AAR is probably at fault. If this has no effect, look elsewhere. A bad vacuum leak will sometimes cause a high pitch whistle sound. Check all the hose's and that the intake manifold is tight.

Yup, somewhere there's a vacuum leak. Since the idle goes up to and then falls my guess is the AAR is working. But there is a cracked hose or injector seal that is letting in all the extra air in. All the hoses, seals must be in good condition so the engine only pulls air though the throttle body.


Geoff

Another suspect is the ignition timing. If it is overly-advanced, that will raise the idle RPMs.

Probably not by as much as this case, though. I'd check for a very sizeable vacuum leak--like one of the ~1/2" hoses fell off.

--DD

probably one of the vacuum hoses came off ...

Andy