Idle Speed: Description and Operation

The PCM controls the engine idle speed by controlling the position of the Idle Air Control (IAC) valve. The IAC valve is a bi-directional motor driven by two coils The PCM sends pulses (steps) to the IAC valve to move a pintle in and out of a passage in the throttle body When the PCM extends the pintle, the idle speed decreases. The idle speed increases when the PCM retracts the pintle. This method allows a more accurate control of the idle speed, and a quick response to changes in the engine load. If the idle speed is too low, and the PCM is unable to adjust the idle speed by increasing the IAC pintle position, DTC P0506 will set