Minimum Air Rate - Fuel Injection Only

The throttle plate stop screw or minimum air rate adjustment should not be considered the minimum idle speed, as on other fuel injected engines. Low internal friction and provision for slight production variations and various operation altitudes resulted in a calibrated minimum air rate which is too low to allow most engines to idle. The adjustment is pre-set at the factory and no further adjustment should be necessary.


If there is a complaint of high idle speed, vacuum leaks should be considered the most likely cause. Because the Electronic Control Module (ECM) controls Idle Air Control (IAC), it is even less likely that a stalling complaint would be due to incorrect minimum air rate. If either occurs see DIAGNOSIS AND TESTING PROCEDURES/TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM/STALLS-ROUGH,UNSTABLE OR INCORRECT IDLE.


If the minimum air rate is still suspected, be sure the 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.


The minimum air rate may be checked using the following procedure:


1. Block drive wheels and apply parking brake.
2. Connect "Scan" tool.
3. Start engine and allow to reach operating temperature and "Closed Loop."
4. Automatic transaxle only - shift to drive and back to NEUTRAL.
5. With A/C and all electrical accessories "OFF," transaxle in NEUTRAL, "Scan" power steering pressure switch input. It should be "OFF" or "NORMAL." . Allow idle to stabilize.
6. "Scan" IAC valve counts - if within specifications (see Powertrain Management/Computers and Control Systems/Specifications/Mechanical), throttle plate stop screw adjustment is acceptable. It is important to allow the idle speed to stabilize to assure correct counts are determined. If counts are too low, check for intake air (vacuum) leaks at hoses, throttle body, and intake manifold. Check for damaged throttle lever and correct as necessary.


If no vacuum leaks or other cause of excessive air into the intake are found, continue to Throttle Plate Stop Screw (Minimum Air Rate) Adjustment Procedure. If counts are too high, check for damaged throttle lever or airflow restriction by the throttle plate. If no problem is evident, remove inlet air duct at the throttle body and clean residue from inside of throttle body bore and from edges of throttle plate.


Do not use solvents containing Methyl Ethyl Ketone. "Scan" IAC valve counts, per the preceding procedure. If counts are still too high, refer to "Throttle Plate Stop Screw (Minimum Air Rate) Adjustment Procedure."

THROTTLE PLATE STOP SCREW (MINIMUM AIR RATE) ADJUSTMENT PROCEDURE

NOTE: It is extremely unlikely that this adjustment will ever be necessary on a throttle body that has not been tampered with after production!

1. Remove throttle plate stop screw plug.
2. Back 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.
3. Turn the stop screw in until it just contacts the throttle lever.
4. Turn the stop screw 1 1/2 turns further.

NOTE: If IAC valve counts are still out of the acceptable range after the idle has been allowed to stabilize, the adjustment may be tailored as follows:

More throttle plate opening = lower IAC valve counts. Less throttle plate opening = higher IAC valve counts. If necessary to change the adjustment more than one half turn either way, other causes of incorrect idle speed should be checked.