Idle Speed/Throttle Actuator - Electronic: Description and Operation

Idle Air Control Valve:

All engine idle speeds are controlled by the ECM/PCM through the Idle Air Control valve mounted on the throttle body. The ECM/PCM sends voltage pulses to the IAC motor windings causing the IAC motor shaft and pintle to move in and out a given distance (number of steps) for each pulse, (called counts).

This movement controls airflow around the throttle plate, which in turn controls engine idle speed, either cold or hot. IAC pintle position counts can be seen using a "Scan" tool. 0 counts correspond to a fully closed passage, while 140 counts or more (depending on application) corresponds to full airflow through the throttle body bypassing the throttle blade.