MINIMUM IDLE SPEED ADJUSTMENT PROCEDURE IS OUTLINED

VEHICLES AFFECTED: 1987 J AND L 2.0L ENGINE (VIN CODE 1)

CORRECTION: "THE PRELIMINARY SERVICE MANUAL" procedure of locating the IAC pintle by grounding the diagnostic terminal (ALDL connector) is NOT APPLICABLE to this engine calibration and SHOULD NOT BE USED.

Use one of the followinq procedures.

Update: Finalized Service Manual Procedure ------------------------------------------ For the "idle air passage plugging tool" procedure, as defined in the Service Manual, two service tools (or their equivalent) can be used. They are J-36377 and BT 8528A (new).

Optional Procedure:

An optional procedure for setting minimum idle speed adjust for a lower TBI assembly replacement is defined as follows: This "optional procedure" can be used when the idle air passage plugging tool is not available.

REVISED MINIMUM IDLE SPEED ADJUSTMENT PROCEDURE FOR 2.OL (VIN 1) ENGINE

This adjustment should be performed onlv when the throttle body assembly has been replaced. Complete TBI units are factory adjusted and should not be reset in the field. Engine should be at normal o2erating temperature before making adjustment.

IMPORTANT

The throttle stop screw, used for regulating minimum idle speed, is adjusted at the factory. The screw is covered with a plug to discourage unauthorized adjustments. However, if it is necessary to gain access to the Minimum Air Adjustment Screw the following procedure eliminates removal of the TBI unit from the manifold.

1. Remove TBI bonnet and gasket.

2. Pierce the Minimum Air Adjustment Screw plug with an awl and apply leverage to remove it.

3. Connect a "Scan" tool to monitor IAC counts and engine RPM.

4. Set parking brake and block drive wheels.

5. Put transmission in park (neutral on manual transmission), start engine and allow engine RPM to stabilize.

6. Create a vacuum leak by removing a vacuum hose to a manifold vacuum source. Allow vacuum leak to remain until "O" IAC counts are shown on "Scan" tool.

7. With IAC counts at 0, disconnect Idle Air Control Valve electrical connector.

8. Reconnect vacuum hose.

9. On vehicles with automatic transmission, place selector lever in D (drive) before making adjustment.

10. Adjust Minimum Air Adjustment Screw to obtain 650 plus or minus 25 RPM.

11. Turn ignition "OFF" and reconnect IAC valve electrical connector.

12. Use silicone sealant, or equivalent, to cover Minimum Air Adjustment Screw.

13. Install TBI bonnet (replace gasket if necessary).

This service bulletin is for information only.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.