ROUGH IDLE/COLD START STALL NEW CALIBRATION PROM. GMC Truck S15 Pickup - 4WD 1989

For 1990-2009 cars

# ROUGH IDLE/COLD START STALL NEW CALIBRATION PROM

#### SUBJECT: ROUGH IDLE/STALL AFTER COLD START

#### MODELS: 1988-91 S/T TRUCK W/4.3L AND AUTOMATIC TRANSMISSION (4L60)

#### APPLICATION:

1988-91 4.3L Auto. S/T Truck W/Calif. Emission (NB2)

1988-90 4.3L Auto. S/T Truck W/Federal Emission (NA5)

#### CONDITION:

---------- Some of the above trucks may exhibit a rough idle, sag or stalling condition after cold start-up at intermediate ambient temperatures of 30-70 degrees F. This condition may be most noticeable while performing a Park to Drive/Reverse shift. The condition improves as the engine reaches normal operating temperature.

#### Cause:

------ The condition is due to low idle speeds and/or lean air/fuel ratios after cold start-up.

#### CORRECTION:

------------ To correct this condition install a new service calibration PROM which revises warm-up idle speeds. The new PROM will also raise the normal con- trolled idle speed from 500 RPM to 525 RPM in drive. Reference the chart below for the proper PROM application.

#### SERVICE PARTS INFORMATION

Service Broadcast Series Engine Trans. Emissions PROM P/N Prom ID Code ------------------------------------------------------------------------ S/T 4.3L Auto. Calif. NB2 16156045 5931 AWLN S/T 4.3L Auto. Fed./Alt. 16147593 3151 ATBA (NA5/NA6)

#### Note: These PROMs were released to production as follows: The Federal PROM is in all 1991 models. The California PROM will go into production in August, 1990 for 1991 models. Parts are currently available from GMSPO.

#### WARRANTY INFORMATION

Labor Operation: T0500

Labor Time: 0.8 hr.

#### NOTE: Labor Operation is coded to base vehicle coverage in the warranty system.

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.