Idle Speed Adjustments

The throttle plate stop screw, or minimum idle speed, is adjusted at the factory and covered with a plug to discourage unnecessary adjustment. But, if access to the throttle stop screw is necessary, the following procedure eliminates the removal of the Throttle Body unit from the intake manifold.


If there is a complaint of high idle speed, vacuum leaks should be considered the most likely cause. The Electronic Control Module (ECM) controls the Idle Air Control (IAC) valve, and it is less likely that a stalling complaint would be due to incorrect minimum idle speed. If either occurs see DIAGNOSIS AND TESTING PROCEDURES/TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM.


If the Minimum Air Rate is suspected, be sure the Idle Air Control (IAC) valve is not "lost" (not actually at the location indicated by current IAC "counts"). The IAC valve could be "lost" if ECM power has been interrupted with the ignition "ON," or the IAC valve has been disconnected with the engine running since the last reset.


CAUTION: To prevent engines from running at high speeds, be sure that the ignition is OFF and the vehicle is in PARK or NEUTRAL before connecting Idle Air Control (IAC) assembly, or installing/removing idle air passage plugs. Failure to do this may result in vehicle movement, which can result in personal and/or property damage.

Stop Screw Plug Removal:

The Minimum Idle Speed may be checked using the following procedure:


1. Block drive wheels and apply parking brake.
2. Connect a "Scan" tool to the ALDL connector.
3. Remove the idle stop screw plug with an awl.
4. Turn ignition to the "ON" position.
5. Select "Field Service Mode" on the "Scan" tool (see specific "Scan" tool instructions). This causes the IAC valve pintle to seat in the throttle body, blocking air flow. Wait at least 45 seconds, then disconnect the IAC electrical connector. Exit the "Field Service Mode."
6. Place the transmission/transaxle in PARK (A/T) or NEUTRAL (M/T). Start and run the engine until it reaches normal operating temperature, and "Closed Loop" operation is attained.
NOTE: It may be necessary to hold the throttle open slightly to maintain idle speed. Make sure all accessories are "OFF," and throttle and cruise control cable are not holding the throttle open.
7. Select "Engine speed" on the "Scan" tool, and note engine speed.
8. See SPECIFICATIONS/MECHANICAL for idle speed values, and adjust the idle stop screw if necessary.
9. Turn "OFF" the ignition and reconnect the IAC electrical connector.
10. Reset the IAC valve. See IDLE AIR CONTROL (IAC) RESET PROCEDURE under ADJUSTMENT PROCEDURES.
11. Cover the idle stop screw with silicone or similar sealant.
12. Disconnect "Scan" tool and remove blocks from the drive wheels.