idle up, idle down
 

Help, When my 84' 944 warms up, and I take my foot off the gas at a traffic light, and I push the clutch in, my idle drops to 100-200 and the surges to about 900 and back down to 100 and so on... and so on... (if it does not stall). It never has a problem restarting, but the up/down continues until I am on the gas pedal again. While driving, there is NO up down only while stopped.

Either the throttle plate mechanical stop or the Throttle Position Switch are out of adjustment.

Remove the throttle body. Loosen the Throttle Position Switch. Loosen the jam nut on the mechanical stop screw. Back the stop screw out until it does not touch the mechanical stop arm. Verify that the throttle plate is fully closed. (Hint: This is a real good time to clean the throttle body!)

With the throttle plate fully closed, turn the mechanical stop screw in until it just touches the stop arm. Turn the mechanical stop in an additional 1/2 turn and tighten the lock nut.

Now you can set the TPS so the micro switch makes a soft 'click' just as the throttle plate comes off the seat.

Reinstall the throttle body and you're done.

Don't forget pesky vacuum leaks can cause similar disturbances, though usually not going all the way down to 100rpms.

search - surges

Good advise, but you need to put your model and year in the sig line.