My car idle sometimes changes.It will idle high about 1100 rpm for weeks at a time and then one day it will idle about 500 rpm barely stays running. Stalls sometimes. It will run this way for aweek or so then back to high idle.The engine light is always on.

If you have not run the fault codes then that would be a good place to start. It will save you money as it will pinpoint the failing sensor.

Idling is too slow at 500 rpm.......think about at least 650 rpm to charge the battery and keep up inertia for better take-off power.
Find out how to increase rpm,whether it's a screw-stop adjustment or a timing problem. don-ohio (:^)

I would look at the cold start injector first and work from there.

Without checking your car physically, its not possible to give you any idea what it could be or not

You engine is TBI, It uses a MAP sensor check the vacuum line for crack and make sure yo have a good seal, The distributor also check and make sure the pick up does not have corrosion which causes the relutor to stick. As for the EGR it would cause a misfire, and yes the do fail. I am sticking with the IAC as a problem its a stepper motor and has a high failure rate, chack also the ECT (engine coolant temp sensor) for corrosion that gives false reading.

Try cleaning the throttle body plates with throttle body cleaner.Also check for vacuum leaks around the intake gaskets.You can also check for codes.Sometimes you can have codes and not get a check engine light.Hope this helps.Good luck.

have you checked for vacuum leaks?

HELLO. WELL YOUR ALMOST RIGHT,. WHAT YOU NEED TO DO . IS CHANGE YOUR MAP. CENSER'S . AND THAT SHOULD DO THE TRICK . WELL HOPE THIS HELP'S YOU , GOOD LUCK

Try changing the throttle position sensor. It varies voltage to change rpm and if it is wet and shorted it will set maximum rpm.

i would tell the dealer u want a second opion bescause my 2004 cavlier idles sometimes high it it turned out to be the rpm were wrong