Idle Air Control (IAC) Valve

Idle Air Control Valve.:

The IAC valve is located in the throttle body on both engines. The idle speed is controlled by the PCM using the IAC valve. The IAC valve consists of a two-coil stepper motor that moves a pintle valve in and out from the seat controlling the amount air bypassing the throttle plate. The PCM controls the IAC valve by supplying ignition voltage or ground to any of the four circuits of coil "A" or coil "B". When one circuit of a coil is supplied ignition voltage the other is supplied ground. Coil "A" and coil "B"are independent of each other, however both must be functional for the valve to move correctly. Retracting the IAC valve allows more air to flow into the intake manifold which raises engine speed. Extending the IAC valve allows less air to flow into the intake manifold lowering engine speed. The determination of how much air is allowed into the engine is based on engine speed, A/C relay command, ECT, TP angle, transaxle range switch position and transaxle shifting. Once the PCM learns the IAC position for A/C relay On and A/C relay Off, it can retard or advance ignition timing to finely adjust the idle speed without moving the IAC valve.