Idle Speed: Description and Operation

The control module controls idle speed with an Idle Air Control (IAC) valve. The desired RPM is based on sensor inputs and the actual engine RPM. Four circuits are used in order to control the IAC valve, allowing a precise amount of air into the intake manifold. In order to increase the idle RPM, the control module will command the valve pintle to move away from its seat allowing more air to bypass the throttle plate. To decrease RPM, the control module commands the IAC pintle to move closer to its seat causing a lower airflow to bypass the throttle plate. A scan tool will display the control module commands to the IAC valve in counts. The higher the counts, the more air is allowed to bypass the throttle plate. Lower counts indicates less air is commanded by the control module.