I call this surging and it can happen all the time, only when engine is cold, or when the engine is warm. Yours appears to be only when warm. Here is a list of things to look for:
vacuum leak - could be a hose cracked, broken, or loose
bad or plugged IAC valve - the Idle Air Control valve can be taken off and cleaned
air in the cooling system - with the engien warm crack open a bleeder on the cooling system (antifreeze not freon) Remove the air from the system. A possible leak in the system could be allowing air in.
Check the EGR valve
bad O2 sensor
bad MAF sensor
Start at the top and work your way down.
Wednesday, July 18th, 2007 AT 8:31 AM