Idle Speed/Throttle Actuator - Electronic: Description and Operation

The idle air control (IAC) system is designed to control engine idle speeds while preventing stalls due to changes in engine load. The IAC assembly, mounted on the throttle body, provides control of bypass air around the throttle plate by extending or retracting a conical valve to divert air around the throttle plate. If RPM is lower than desired, more air is diverted around the throttle plate to increase RPM. If RPM is too high, less air is diverted around the throttle plate to deacrease RPM.
At idle speeds, the ECM calculates the desired position depending on battery voltage, coolant temperature, engine load and engine RPM. If RPM drops below a specified RPM and the throttle plate is closed, the ECM will sense a near stall condition and will calculate a position based on barometric pressure to prevent stalls.