Kula

Hi all - I'm having a problem with my '80 911 SC that I haven't been quite able to diagnose yet. And before I go tearing into the engine compartment, thought that I'd see if anyone else had any ideas. The engine is completely stock and there haven't been any modifications to the engine nor recent work.

The problem: engine idle is stable at ~ 900 RPM when the engine is cold, but after about 30 minutes of driving, the engine idles at ~ 2600 rpm at while I'm waiting at lights. There is no hunting for idle speed - it starts at about 950 then moves steadily up to 2600 rpm. Even after sitting at work for about 10 hours, the engine idles at 2600 and will return to normal only after sitting in the garage overnight.

I've checked for vacuum leaks but haven't found anything obvious.

Anyone have a similar problem on good ideas?

Thanks!

autofil

Hi!
This could be the same problem I had with my 86 Carrera 3.2.
My car did have similar problems, and was caused by a problem with the idle switch. (located on the backside of the throttle body).
Is this the same on the SC?

This micro switch indicates your throttle in idle position and in my car the switch was pressed to hard and then lost contact and the engine did not detect that the the throttle was in idle position. A small adjustment on the throttle to reduce the force to the switch and my idle was OK.

Drew Theodore

When your rpms are high, go back in the engine bay and you should see the black throttle cable coming from the drivers side up and over where the air enters the air filter cover. Wiggle the cable around a little and see if that helps.

Kula

I'll look at the throttle switch and see if that has anything to do with it (maybe it sticks when it gets hot?).

I don't think that its the throttle cable as I would think that it would always stick if it were binding rather than only when it's hot.

Thanks for the help. I'll keep poking around to see if I can find a cause.

944ZEN

There's no Throttle Switch on the SC', since it's all Mechanically controlled injektion system (K-Jetronic) vs. the carras Motronic controlled system.

The high idel could be the "Warm Up Regulator" That controls the Back pressure on the Fuels distibutor. The WUR is respnsible for adjusting system pressure according to the engienes temperature. This serves to enrichen the Mixture during Warm up. Inside the WUR is a valve that is supposed to close more and more as the temperarature goes up. If that's deffekt, it will not adjust the mixture correctly.

It could also bee the AUX air valve is not closing. It supplies extra air at low temp to raise teh idle speed, in conjuction with the WUR.

But have you tried adjusting the idle speed screw, on the side on the Throttel boddy, next to the throttle linkage. ???