Idle Air Control (IAC) System

The IAC system consists of an electrically controlled motor (actuator) which positions the IAC valve in the air by-pass channel around the throttle valve. The IAC valve is a part of the throttle body casting. The ECM calculates the desired position of the IAC valve based upon battery voltage, coolant temperature, engine load and engine speed to control idle speed while preventing stalls due to engine load changes.

If engine speed is lower than desired, the ECM activates the IAC motor to retract the IAC valve. When the IAC valve is retracted, more air is diverted around the throttle valve to increase engine speed. If engine speed is higher than desired, the ECM activates the IAC motor to extend the IAC valve. When the IAC valve is extended, less air is diverted around the throttle valve, decreasing engine speed. If engine speed falls below a preset level and the throttle valve is closed, the ECM senses a near stall condition. To prevent stalling, the ECM will calculate an IAC valve position based upon barometric pressure.