GM 17112866 Actuator,Throttle Body Idle Speed Control

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The Idle Control (IAC) system is responsible for controlling engine idle speeds and preventing stalls caused by changes in engine load. The system works by allowing a controlled amount of air to bypass the throttle blade via the IAC valve. The valve consists of a rotating shutter that is held in a neutral position by opposing springs. The PCM controls the valve using two control circuits, one to open the valve and one to close it. By modulating the frequency of the control signals, the PCM can adjust the idle speed. To test for IAC-related problems, preliminary checks should be done to ensure proper connections, inspect the wire harness for damage, check for a restricted air intake system, and look for vacuum leaks. If a scan tool is available, the RPM can be commanded while monitoring the engine speed. If the IAC valve responds correctly, it is functioning properly. If a scan tool is not available, resistance tests can be performed on the IAC terminals. If the resistances are within specifications, the IAC circuits should be checked for continuity back to the PCM. If everything is functional, the PCM may be faulty. To remove and install the IAC motor, the necessary steps should be followed for the specific engine type. After installation, minimum air, throttle position sensor (TPS), and idle learn adjustments should be performed.