In the Throttle body the butterfly is completely closed at idle. Above and below the butterfly is a channel or bypass. This bypass is the only way for air to enter the manifold, during idle. The butterfly or throttle plate only opens when you touch the gas pedal. In this channel/bypass is a plunger for controlling the airflow rate. A motor moves the plunger in & out. This plunger/motor combo is the Idle Air Control Motor (IAC). Air for start-up and idling is controlled by the PCM. It tells the IAC how much to open/close to let air into the intake manifold.
Symptoms of a bad IAC: hunting behavior of the rpms, extremely high or low idle speeds.
Therefore your problem is most likely one of two things: a dirty or frigged IAC or a faulty TPS throttle position sensor. I would suggest spraying the hell out of the throttle body with electrical cleaner and spray up into the IAC passage.
94 Black Laredo 4-Liter with QuadraTrac (42RE trans & NP249 TC) 200,000 + miles purchased new
88 Cherokee 2-door with 5speed manual 139K miles(deceased) purchased new
Last edited by greasefingers; 07-26-2006 at 08:03 PM..