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Chart C-2A, Idle Air Control (IAC) Valve Check: Notes

ECM/PCM controls engine idle speed with Idle Air Control (IAC) valve. To increase idle speed, ECM/PCM grounds the OPEN solenoid within the IAC valve. A plate within the IAC valve opens and allows air to by-pass throttle plate. ECM/PCM regulates fast idle speed by increasing the IAC valve opening of the air by-pass port. To decrease idle speed, ECM/PCM grounds CLOSE solenoid within the IAC valve, which allows less air to by-pass throttle plate. ECM/PCM regulates slow idle speed by decreasing the IAC valve opening of the air by-pass port.

NOTE: Test numbers refer to numbers on diagnostic chart.
  1. Check for open in power feed to IAC valve.
  2. Checks IAC valve CLOSE circuit.
  3. Checks IAC valve OPEN circuit.
  4. Checks for an open or short to ground in Black/Blue wire, a faulty IAC valve or a faulty ECM/PCM.
  5. Checks for an open or short to ground in Black/White wire, a faulty IAC valve or a faulty ECM/PCM.
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