Pavegeno928

Having two issues. The most recent one for the last few months: When I come off the throttle, the RPMs drop to 2000 RPM with clutch in and throttle closed. If I tap the throttle, the RPMs drop back down to idle. Does this almost constantly. Mechanic has had the engine out and verified all good from the transmission back.

The other problem is one I've had for a few years but only when the engine is warmed up a bit: I get a fluctuating RPM of +/-200 rpm at idle when warm. Doesn't do it all the time, just after the car has warmed up.

Any thoughts? vacuum line? Is there a throttle position sensor? I have replaced the DME relay. Spark plug wires are only a few years old and rotor/distributor are new as well as the coil.

Thanks...

Amber Gramps

Sounds to me like your Idle Control Valve is sticking.

You can pull it off and clean it's internal moving valve with Brakleen or carb cleaner. Plugged in with Key On/Engine Off it should make a buzzing sound.

cairo94507

Nice wiener doggie.

mk85911

I had a similar issue with RPM sticking at about 2000 RPM and the problem was the bracket which holds the throttle cable in place in the engine bay just short of the throttle linkage. The throttle comes out of the firewall and loops around to the bracket, which had deteriorated to the point that the cable shifted a fraction of an inch and hung up just enough to cause a high RPM. I simply tightened it up with a lock tight fastener, and that solved the problem. This has held up for about six years, and cost less than a penny for parts--my best Porsche fix ever!

Pavegeno928

Thanks for the inputs all!

NineMeister

Check the mechanism on the throttle body. The main linkage pulls on a secondary lever which has some play before it opens the throttle plate. This secondary lever actuates the idle switch; sometime this lever is stiff and seizes up on the throttle shaft which then allows the throttle to close without the additional movement onto the idle switch. If seized a soaking with brake cleaner and WD40 usually releases the movement.

weneversleep

I'm having the same problem on my newly purchased 74 911. Thanks for this thread; I now have some ideas to try! I thought it might be an air leak somewhere in the intake.