Hot Idle Speed hunting

[gdee123]

Does the following ring any bells?

Car starts well, and idles at 950 almost immediately, but when its good and hot, the idle speed goes to 2200. Loading the engine/clutching at stationary causes it to go back to 950, but a touch of the throttle sends it back to 2200. Its no problem when driving at speed ( and what speed!), accelerates wonderfully, but is difficult in traffic, especially pulling from low revs in 2nd or 3rd, mad judderring until say 2500+ revs, then its like a sewing machine again. Distributor Vacuum advance is connected to the vac line.

any ideas?.

Garrett

1973 911S 2.4L w MFI

[Cornpanzer]

Its possible that your throttle shafts are leaking air and causing a slight lean condition at idle. I run into this especially when its cool ambient temps with my MFI. The Idle creaps up until it hits the 1500 rpm fuel shutoff, drops back down and repeats. Very annoying in traffic!

[Eric911S]

Hello: To check for air leaks use some WD40 and spray around the heads,butterfly shafts and the base of the stacks. If you have a leak it will either slow the engine down or blow a little white smoke. Good luck. Thanks Eric

[gdee123]

Its 11 at night here, so I'll follow your advice tomorrow. Many thanks for both your replies!!

Garrett

1973 911S 2.4L w MFI

[spydr32000]

Sounds to me like you have a distributor problem! Check for any vaccuum leaks or a cause of lean running, but most likely you will end up with your distributor getting rebuilt.

[gdee123]

It was the fuel shut-off solenoid microswitch - not making at the throttle stop: pure luck that I found it! She's running beautifully now.

Thanks for the replys.

Garrett

1973 911S Targa

[Cornpanzer]

That switch does nothing unless the engine is over 1500rpm so Im not sure how this affected the idle?

[gdee123]

The problem was that the engine wouldn't return to a normal idle speed when downshifting to slow down/stop for traffic, junctions etc. but stay at 2200 rpm in neutral, ie from > 1500; also performance at moderate speeds ( in town etc.) where my foot is on and off the throttle was judderrry, I guess because revs are 1500+ typically, and when throttle was off, the engine was overrevving.

In any case having driven out of town and back into town last night for 45 minutes, the problem was gone.

Hope it stays that way!!

Garrett