DTC P0507: Idle Control System - High Rpm: Description

WARNING: This page is about a different car, the 2001 GMC Savana, 2001 Chevrolet RV Cutaway, 2001 Chevrolet Cutaway, and 2001 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.

Idle Air Control (IAC) valve is located in throttle body of both sequential multiport fuel injection and multiport fuel injection systems. IAC valve consists of a movable pintle, driven by a gear attached to an electric motor called a stepper motor. IAC valve motor is a two 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 Powertrain Control Module (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. PCM counts steps 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 airflow around throttle plate when throttle is closed. To determine desired position of IAC pintle at idle or during deceleration, PCM refers to the following inputs:

Engine RPM.
Battery voltage.
Air temperature.
Engine Coolant Temperature (ECT).
Throttle Position (TP) sensor angle.
Engine load.
Vehicle speed.

When ignition is turned off after an ignition cycle, PCM will first seat IAC pintle in air bypass bore, and then retract IAC pintle a predetermined amount of counts to allow proper amount of air to bypass throttle plate for engine start-up. This procedure is known as an IAC reset.