Idle Speed/Throttle Actuator - Electronic: Description and Operation

IDLE AIR CONTROL (IAC) VALVE




The idle air control (IAC) valve is attached to the underside of the throttle body with 4 bolts. The IAC valve enables the powertrain control module (PCM) to easily control the engine idle speed by precisely metering the engines air intake at closed throttle. The IAC valve opens and closes the idle air bypass passage according to signals from the PCM. The IAC valve contains an engine coolant passage that enables the IAC valve to operate more efficiently at cold temperatures. The PCM determines the correct engine idle speed by using input from various sensors and switches in order to assess the engine status and requirements.

Operation




The PCM uses the IAC valve in order to control the 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.

The IAC valve contains an engine coolant passage that enables the IAC valve to operate more efficiently at cold temperatures. The IAC valve enables the PCM to easily control engine idle speed by precisely metering the engine's air intake at closed throttle.