ENG. STALL AFTER HOT RESTART COLD START AND COLD ENG. HES.

SOME 1987, A, J OR L MODELS AND 1988 L OR W MODELS EQUIPPED WITH A 2.8L V-6 ENGINE MAY EXPERIENCE A COLD START STALL, A STALL AFTER START WITH A WARMED UP ENGINE OR A STALL DURING DECELERATION. A 5 SPEED MANUAL TRANSMISSION L OR J CAR MAY ALSO EXPERIENCE A HESITATION DURING ACCELERATION PRIMARILY WHEN THE ENGINE IS COLD (AMBIENT TEMPERATURES OF 4 TO 21 DEGREES CELSIUS). THIS HESITATION MAY ALSO BE EXPERIENCED DURING TRANSMISSION GEAR SHIFTS.

A REPEATED STALL AFTER HOT RESTART MAY BE CAUSED BY RESIDUE ACCUMULATING INSIDE THE THROTTLE BODY BORE, BEHIND THE THROTTLE PLATE, WHICH LIMITS THE AIR FLOW PAST THE THROTTLE PLATE IN THE IDLE POSITION. THE HESITATION CONCERN MAY BE DUE TO A LEAN ELECTRONIC CONTROL MODULE (ECM) FUEL CALIBRATION. THE COLD START STALL MAY BE DUE TO A LEAN ECM CALIBRATION, LOW ENGINE IDLE SPEEDS, THE LOSS OF FUEL PRESSURE, OR LOOSE ELECTRICAL CONNECTIONS AT THE IGNITION COIL AND/OR THE MASS AIRFLOW SENSOR.

THE AFOREMENTIONED CUSTOMER COMMENTS MAY BE REPAIRED AS FOLLOWS:

1. PERFORM NORMAL SERVICE PROCEDURES AS OUTLINED IN THE SHOP MANUAL FOR THE REPAIR OF ENGINE STALL OR HESITATION.

2. VERIFY THAT ALL ELECTRICAL CONNECTIONS SUCH AS AT THE IGNITION COIL AND MASS AIRFLOW SENSOR ARE SECURE.

NOTICE: LOOSE/POOR ELECTRICAL CONNECTIONS AT ALL SENSORS AND ECM METRI PAK CONNECTORS CAN BE A PROBLEM ANYWHERE ON THE ENGINE. INTERMITTANT CONNECTION CAN PRODUCE STALLING.

3. VERIFY THAT THERE ARE NO ENGINE VACUUM LEAKS AT THE MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR, POSITIVE CRANKCASE VENTILATION (PCV), EXHAUST GAS RECIRCULATION (EGR), OR OTHER SYSTEMS.

4. VERIFY THAT THE FUEL SYSTEM IS FUNCTIONING PROPERLY AND HAD PROPER FUEL PRESSURE. (REFERENCE BULLETIN #87-628-105).

5. CLEAN THE THROTTLE BODY BORE AS SPECIFIED IN SERVICE BULLETIN #87-628-109

6. MEASURE THE MINIMUM IDLE SPEED AND THROTTLE POSITION, AND ADJUST TO SPECIFICATION IF REQUIRED (REFERENCE BULLETIN # 87-628-109).

7. REPLACE THE ECM MEMCAL (SEE ATTACHMENT A), USING THE FOLLOWING INSALLA- TION PROCEDURE:

A. DISCONNECT BATTERY POWER. B. INSTALL NEW ECM MEMCAL CALIBRATION. C. RECONNECT BATTERY POWER. D. START VEHICLE WITH AC/DEFROSTER OFF AND POWSER STEERING NOT CRMPED. E. ALLOW VEHICLE TO IDLE IN DRIVE FOR 6 MINUTES AND UNTIL THERMOSAT HAS OPENED. THIS WILL FACILITATE LEARNING OF BASE IDLE. F. RETURN VEHICLE TO SERVICE.

NOTICE: IT IS INAPPROPRIATE TO REPLACE THE MEMCAL AND RETURN THE VEHICLE TO THE CUSTOMER WITHOUT PROPERLY COMPLETING THE PREVIOUS SERVICE INSTRUCTIONS (ITEMS 1-6).

USE APPLICABLE LABOUR TIME AND OPERATION NUMBERS.

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.