Operation

The powertrain control module (PCM) uses the IAC valve in order to control engine idle speed. The PCM communicates with the IAC valve by varying the ON time of a repeating ON/OFF (duty cycle). A magnet inside the IAC valve operates a rotary valve that controls the opening of the idle air (bypass) passage in the throttle body. The idle air passage allows air to enter the engine without passing over the throttle valve. The strength of the magnet in the IAC valve is related to the current flow in the IAC circuit.

The PCM increases the ON time of the IAC valve command in order to increase the idle air passage opening. A larger idle air passage opening allows more air to enter the intake resulting in an increase in engine speed.