Idle Air Control Valve

WARNING: This page is about a different car, the 2003 GMC Sierra and 2003 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The engine idle speed is controlled by the Idle Air Control (IAC) valve. IAC valve is mounted on throttle body. IAC valve pintle moves in and out of an idle air passage bore to control air flow around the throttle plate. The IAC valve consists of a movable pintle, driven by a gear attached to an electric motor called a stepper motor. The stepper motor is capable of highly accurate rotation or of movement, called steps. The stepper motor has 2 separate windings that are called coils. Each coil is supplied current by two circuits from the PCM. When PCM changes polarity of a coil, the stepper motor moves one step. The PCM uses a predetermined number of counts to determine the IAC pintle position. Observe IAC counts with a scan tool. The IAC counts will increment up or down as the PCM attempts to change the IAC valve pintle position. An IAC Reset will occur when the ignition is turned off. First, the PCM will seat the IAC pintle in the idle air passage bore. Second, the PCM will retract the pintle a predetermined number of counts to allow for efficient engine start-up. If engine idle speed is out of range for a calibrated period of time, an idle speed related DTC will set. To diagnose, see SELF-DIAGNOSTICS - 4.3L SIERRA & SILVERADO article.