A friend is having a weird problem with his 3.1 he can rev the engine, the cable returns to the stop immediately as you would expect but the rpms gradually come back down. And the car is idling at about 1500rpm at the minute.

He says when he is driving it holds the revs too so sometimes he doesn't even have to touch the accelerator pedal! TPS? Vacuum leaks?

 

IAC or vacuum leak.

RBob.

 

I second IAC, if it’s stuck closed it’ll rev super high, stuck extended and the car will start then die without gas. Have a friend ground the ALDL terminal while you have a hand on the IAC to see if you can feel it buzz/hum. Unscrew it from the manifold (don’t lose the gasket!) and see if you can depress the pintle at all. Give it and the throttle body a clean while you’re in there with some intake manifold cleaner. Be careful not to get the cleaner anywhere other than the tip of the pintle (spray from above).

If the IAC buzzes with the ALDL grounded and is nice and clean, then probably a vacuum leak.

I only harp on the IAC because I noticed something similar when I was testing some things with the IAC disconnected from the ECM when it was fully closed.