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

Fig 1: Chart C-2C Circuit Diagram (Storm & Storm GSi)

Courtesy of GENERAL MOTORS CORP.

Fig 2: Chart C-2C Flow Chart (Storm & Storm GSi)

Courtesy of GENERAL MOTORS CORP.

The ECM controls engine idle speed with the IAC valve. To increase idle speed, ECM retracts IAC valve pintle from seat, increasing air by-passing the throttle bore. To decrease idle speed, ECM extends IAC valve pintle toward the seat, reducing air by-passing throttle bore. A "Scan" tool will read ECM commands to the IAC valve in counts. Higher counts indicate more air by-pass (higher idle). The lower counts indicate less air allowed to by-pass (lower idle).

1. Using a "Scan" tool to retract and extend IAC valve, the valve should move smoothly within specified range. If commanded idle speed (IAC extended) is too low (less than 700 RPM), engine may stall. This may be normal and would not indicate a problem. Retracting IAC beyond its controlled range (greater than 1500 RPM) will cause a delay before RPM decreases. This is also normal.
2. This test uses "Scan" tool to command the IAC controlled idle speed. The ECM issues commands to obtain idle speed. Node lights should flash Red and Green to indicate a good circuit. While sequence of color is not important if either light is OFF or does not flash Red or Green, check circuits for faults, beginning with poor terminal contacts.