Chart C-2C Idle Air Control (IAC) System Check: Notes

ECM controls IAC valve by sending voltage pulse to the appropriate servo winding to move motor shaft and valve pintle in or out. ECM voltage pulses are called counts. To increase idle speed, ECM retracts IAC (higher counts) to allow more air to by-pass the throttle plate. To decrease idle speed, ECM extends IAC (fewer counts) to decrease by-pass air.

1. IAC tester is used to extend and retract IAC valve. Valve movement is verified by an engine speed change. If no change in engine speed occurs, valve can be retested when removed from throttle body.
2. Between 700 RPM and about 1500 RPM, engine speed should change smoothly with each flash of tester light in both extend and retract modes. If IAC is retracted beyond the control range (about 1500 RPM), it may take many flashes in extend position before engine speed will begin to drop. This is normal on certain engines, since fully extending IAC may cause engine stall.
3. Each lamp on the node light should flash Red and Green while IAC valve is cycled. If either light is off or does not flash Red and Green, check circuits for faults, beginning with poor terminal contacts.