DTC P0507: Idle Speed - High: Description

The Idle Air Control (IAC) valve is located in throttle body and consists of a movable pintle, driven by a gear attached to an electric motor called a stepper motor. The IAC valve motor is a 2-phase bi-polar permanent magnet stepper motor that is capable of highly accurate rotation or movement, every time polarity of a winding is changed. This change in polarity can be seen when observing a test light connected between ground or battery voltage and an IAC valve circuit while PCM is attempting to change engine RPM (test light will flash on or off each time polarity is changed). PCM does not use a physical sensor to determine IAC pintle position, but uses a predicted number of counts, one count represents one change in polarity which equals one step of stepper motor. The PCM counts the steps it has commanded to determine IAC pintle position. PCM uses IAC valve to control engine idle speed. It does this by changing the pintle position in idle air passage of throttle body. This varies the airflow around the throttle plate when throttle is closed.

To determine the desired position of IAC pintle at idle or during deceleration, PCM refers to engine RPM, battery voltage, air temperature, engine coolant temperature, TP sensor angle, engine load, and vehicle speed. When ignition is turned off after an ignition cycle, PCM will first seat the IAC pintle in the air bypass bore and then retract it a predetermined amount of counts to allow proper amount of air to by-pass the throttle plate for engine start-up. This procedure is known as an IAC reset.