Idling High or Low
Check Engine Light Step 2 - The idle air control motor (valve) is responsible for controlling the engine idle speed, if this part fails or becomes weak the engine idle speed could become erratic, additionally, this condition may or may not trigger the MIL (check engine, service engine soon light.) Because of the nature of this valve (large air volume processed) it should be serviced when a tune up is performed to remove "coking" which will hinder the valve's performance. To perform a rough check of the idle air control, remove the valve while reconnecting the wiring harness. While observing the valve with a flashlight, turn the key to the "ON" position, (DO NOT START ENGINE.) the valve should move slightly.
Idle Air Control Valve (Off Engine)
Engine Intake Vacuum Leak Step 4 - The air intake boot or tube is used to deliver air to the intake system of the engine. If this tube becomes loose or broken it can leak unmetered air into the engine effectively causing an unbalance (via the mass air flow MAF sensor) in the computer system which can produce fast or slow idle.
Removing Air Intake Boot Step 5 - A throttle bore is used to regulate the volume of air flow the engine consumes. Controlled either by computer or by manual foot pedal this device must be clean and free from coking build up (light tar substance.)
Throttle Bore Service