'80 911SC low idle/stall at running temp

[sigep174]

I recently acquired an '80 911SC Euro. The car seems to be spot on, but has started stalling after the car has reached normal running temp. I have adjusted the idle up a few times thinking that it was simply a loose idle screw, but it seems to be something else.

Thanks,
John

[sigep174]

Is there anything I should add to this to help facilitate some speculation?

[EdT82SC]

May be a vacuum leak. Does your idle drop when you remove the oil filler cap?

[longhornchris04]

sounds like a vac leak messing up the mixture. depending on where it is, the warm-up sequence may mask it.

Another other option is your CDI box is getting flaky - as the temp goes up, the spark energy falls. This should be a problem across the rev range, not just at idle.

[tt_targa]

I have an '83. When I replaced the thermal switch in the right hand cam cover, my idle became a lot more stable.

It is a thermal/mechanical switch that sends a signal to the computer that the car is warm and needs another mixture profile.

Might be the same on an '80 Euro.

ST

[JoeyD911]

Not to hijack, but is that the cam temp sensor, TT?

[sigep174]

Originally Posted by EdT82SC

May be a vacuum leak. Does your idle drop when you remove the oil filler cap?

I will give that a try this evening.

[EdT82SC]

I should have explained a bit more. Removing the oil filler cap simulates a vacuum leak by letting air into the system. If you already have a vacuum leak removing the oil filler cap will have no effect. So normally your idle will drop when you remove the cap. Finding the leak can be a fit more difficult though. Rubber vacuum lines and seals dry out and crack with age. With a nearly 30 year car there are probably multiple leaks.

[Paulporsche]

Check your warm control pressures (WUR).

Also, what type of CDI do you have? There are many reports of certain Permatunes having problems when they get hot.