Cutlass L4-138 2.3L VIN A FI HP (1990)
Throttle Plate - PFI: Adjustments
The minimum throttle valve position (throttle stop screw) adjustment for this engine 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
throttle valve position which is too low to allow most engines to idle. The adjustment is preset 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
"learns" Idle Air Control (IAC), it is even less likely that a stalling complaint would be due to an incorrect minimum throttle valve position. Before
adjusting minimum throttle valve position (throttle stop screw), see DIAGNOSIS BY SYMPTOM and perform ON-BOARD DIAGNOSTICS, refer
to DIAGNOSIS AND TESTING PROCEDURES/TESTING PROCEDURES/ON-BOARD DIAGNOSTICS.
If it is determined that the minimum throttle valve position is suspect, be sure that the IAC valve is not "lost" (not actually at the location indicated by the
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, as described in the GENERAL SYSTEM DESCRIPTION. The minimum throttle valve position may be
checked using the following procedure:
1.
Block drive wheels, and set the parking brake.
2.
Connect the SCAN tool to the ALDL connector.
3.
START the engine and allow it to warm up to normal operating temperature and the system is in "Closed Loop".
4.
With Automatic Transaxle only - shift to DRIVE and then back to NEUTRAL.
5.
Select the Power Steering pressure switch input on the SCAN tool. With A/C and all electrical accessories OFF, transaxle in NEUTRAL, the
SCAN tool should read OFF or NORMAL. If not see COMPUTERIZED ENGINE CONTROLS, to diagnose and repair faulty PSPS circuit
before proceeding. Allow the idle to stabilize.
6.
Select IAC valve display on the SCAN tool, and read IAC valve counts. If between 5-45 counts, the minimum throttle valve position adjustment is
acceptable. It is important to allow the idle speed to stabilize to assure correct counts are determined.
^
If the IAC counts in step 6 are too low, check for intake air (vacuum) leaks at hoses, throttle body and intake manifold, or damaged throttle
lever and correct as necessary.
^
If the IAC counts in step 6 are too high, check for damaged throttle lever or airflow restriction by the throttle valve. If no problem is evident,
remove the inlet air duct from the throttle body, and clean the residue from inside the throttle body bore and from the edges of the throttle
valve using carburetor cleaner and a shop towel.
NOTE: Do Not use a cleaner that contains methyl ethyl ketone. It is an extremely strong solvent, and not necessary for this type of deposit.
Re-check SCAN IAC valve counts. If the counts are still too high, proceed to the following 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.
Removing Throttle Stop Screw Plug
ADJUST
1.
Remove idle stop screw plug.
2.
Back the stop screw out until the 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 1/4 additional turns.
5.
Re-check the adjustment per "Minimum Throttle Valve Position Check".
