Idle Speed: Adjustments

The PCM controls the air entering into the engine with an Idle Air Control (IAC) valve. To increase the idle rpm, the PCM commands the pintle inside of the IAC valve away from the throttle body seat. This allows more air to bypass the throttle blade. To decrease the rpm, the PCM commands the pintle towards the throttle body seat. This reduces the amount of air bypassing the throttle blade. A Scan tool will read the IAC valve pintle position in counts. The higher the counts, the greater the airflow that bypasses the throttle blade.