Idle Speed Adjustments

The minimum throttle valve position (throttle stop screw) adjustment for this engine should not be considered the "minimum idle speed." The adjustment is preset at the factory and no further adjustment should be necessary except when replacing the throttle body. Replacement throttle bodies are supplied with the throttle stop screw cover off and require initial adjustment after installation.

If there is a complaint of high idle speed, vacuum leaks should be considered the most likely cause. Because the Powertrain Control Module PCM "learns" Idle Air Control (IAC), it is even less likely that a stalling complaint would be due to an incorrect minimum throttle valve position. If a controlled idle can not be maintained a Code 35 will be set. Before adjusting minimum throttle valve position (throttle stop screw) check for trouble codes. Refer to COMPUTERS AND CONTROL SYSTEMS/DIAGNOSIS, TESTING AND INSPECTION PROCEDURES/TESTING PROCEDURES/ON-BOARD DIAGNOSTICS.

PROCEDURE:

1. Back the idle stop screw out until an air gap between the screw and the throttle lever can be seen by looking downward from above the throttle body.
2. Turn the stop screw in until it just contacts the throttle lever.
3. Turn the stop screw in 1 1/2 turns further.
4. Shift the transmission gear selector in PARK (A/T) or NEUTRAL (M/T).
5. Block the drive wheels, and apply the parking brake.
6. Connect a "SCAN" tool to the ALDL connector.
7. START the engine and allow it to reach normal operating temperature and "Closed Loop" operation. Run the engine until IAC valve has learned its controlled idle position.
8. Using the "SCAN" tool, observe Idle Air Control (IAC) valve counts.

NOTE: IAC valve counts should be checked with all accessories (A/C, rear defogger, etc.), and engine cooling fan "OFF."

^ With engine stabilized, IAC valve position should be 10 to 15 counts.

9. If the IAC valve counts are out of the acceptable range, the adjustment may be changed as follows:

^ More throttle valve opening = lower IAC valve counts.
^ Less throttle valve opening = higher IAC valve counts.

NOTE: If it is necessary to change the adjustment more than 1/2 turn either way, other causes of incorrect idle speed should be investigated as previously mentioned.