Idle drops at closed throttle
 

I have a 964 engine whose idle hunts just for a second on startup. I can deal with that. But, when you rev the engine and let the throttle go back on its own, the rpm drops to a low value and sometimes it would stall before correcting itself.

I have checked:

1. Fuel mixture using a air-fuel meter and the mixture is 14.x ish, pretty much OK
2. a vacuum check and there is no vacuum leak with a smoke test
3. Checked the functionality of the idle switch and the resistance changes from zero ohms to infinite when I move the throttle by hand (between 2 of the 3 pins)
4. There is sufficient free play in the throttle cable such that it is not binding when throttle pedal is released
5. O2 sensor is new.

What else could I do?

I have a friend who has a similar issue with a 3.6 in a 914. He's told that it can happen with a light flywheel as it confuses the Motronic. (To be clear, any early flywheel is a "light flywheel" on a 3.6.) Let's see if anyone else can give input on that, clearly it's been done many times successfully.

Yes, this is the case here. A patrick motorsports light flywheel is confirmed to be in this set up and most likely causing this issue.

Sounds like a faulty idle control valve?

I have exactly this problem with the 3.6 in my SC. It’s maddening. I’ve upgraded to the latest Steve Wong chip, checked for a little slack in the throttle cable, checked the idle control valve.

The engine needs a little damper to slow the closing of the throttle for the last few degrees.

My balky shifter means that beteeen shift my car will stall. Makes me nuts.