Idle Speed: Adjustments

Early model vehicles
Idle speed is controlled by the Electronic Control Unit (ECU) and is not adjustable. If the vehicle is idling above specified idle rpm check for vacuum leaks and repair as necessary. If the vehicle exhibits erratic idle characteristics, surges or stalls at idle the throttle body should be inspected and cleaned if necessary. Throttle Body Cleaning

Late model vehicles
Idle speed is controlled by the Single Board Engine Controller II (SBEC II) and is not adjustable. If the vehicle idles above specified rpm check for vacuum leaks and repair as necessary. If the vehicle exhibits erratic idle characteristics, surges or stalls at idle test minimum airflow.
If the vehicle fails the minimum airflow test the throttle body should be inspected and cleaned if necessary. Throttle Body Cleaning