2000 Pontiac Grand AM 2.4 ltr standard trans normal idle is 8-900 rpm. Engine check light came on no code showing . Started up and rpm jumped to 2000RPM throttle closed and when on highway RPM increases when clutch depressed to shift. Rpm will not decrease when you lift gas pedal. When you drop it into gear just as you slow down it will drop back to manageable rpm 2000. Replaced Idle Air Sensor cleaned Throttle body and it seemed to be good rpm at 900 drove two miles shut off . When started jumped back to 1500 rpm. All vacumn lines are checked okay. Any one have an idea on this?

The Ignition Control Module (ICM) may be failing. Try replacing it and see if the problem isn't solved. The tachometer ties directly into the ICM. When ICMs start to fail, tachometers can fluctuate all over the place. It's an easy 5 minute job to replace.