Idle Speed

Idle speed is maintained by Idle Air Control (IAC) valve, which is controlled by ECM. Throttle stop screw on throttle body is pre-set at factory and sealed in position. Minimum throttle valve position adjustment is not necessary, but can be checked unless throttle body has been tampered with. If throttle valve setting has been tampered with, replace throttle body assembly. To check minimum throttle valve position:

1. Block drive wheels, and apply parking brakes. Connect scan tester to ALDL diagnostic connector. Start engine, and operate it to normal operating temperature. Engine should be in closed loop operation.
2. On A/T models, shift transaxle to Drive and then back to Neutral. On all models, select power steering switch input using scan tester. Ensure all accessories are off and transaxle is in Neutral. Scan tester should indicate OFF or NORMAL. If scan tester reading is as specified, go to step 4). If scan tester does not indicate OFF or NORMAL, go to next step.
3. Diagnose and repair faulty power steering pressure switch circuit before proceeding with test. Refer to POWER STEERING PRESSURE SWITCH TEST in SYSTEM & COMPONENT TESTING article.
4. Allow idle to stabilize. Select IAC valve display on scan tester, and read IAC valve counts. If IAC count is 5-45 counts, minimum throttle valve position is acceptable. Ensure idle speed is stabilized when checking IAC counts. If IAC counts are too low, go to next step. If IAC counts are too high, go to step 6).
5. Check for vacuum leaks at hoses, throttle body and intake manifold. Check for damaged throttle lever. Repair or replace as necessary. If no vacuum leaks or other causes of excessive air into intake are found, replace throttle body assembly.
6. Check for damaged throttle lever or airflow restriction by throttle valve. If no problem is evident, remove inlet air duct at throttle body and clean residue from inside throttle body bore and from edges of throttle valve using carburetor cleaner and shop towel.
   NOTE: DO NOT use carburetor cleaner containing methyl ethyl ketone.
7. Recheck IAC counts using scan tester. If counts are still too high, check minimum throttle valve position stop screw (not adjustable). If signs of tampering are present, replace throttle body assembly.