RPM's revving

I have a 1991 Eagle 2000 GTX 16 valve dohc (Mitsubishi engine) std transmission & 178,000 km's.

If the car is sitting idling, the rpm's will rev up and down but will drive normal. When you come to a stop and have the clutch in, the revving will start again until you start moving.

Additionally I've noticed that when you take you foot off the gas pedal and the car slows to a slow speed, it will jerk. I don't know if the two are related or not.

Twice I have had to the mechanic to try and fix but any readings taken from the computer will not identify any problems. Thought it was the mass air flow center & a replacement was installed and did not fix the problem.

I'd really appreciate any help I can get