1988-91 4.3L Auto. S/T Truck W/Calif. Emission (NB2)
1988-90 4.3L Auto. S/T Truck W/Federal Emission (NA5)
---------- 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.
------ The condition is due to low idle speeds and/or lean air/fuel ratios after cold start-up.
------------ 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 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)
Labor Operation: T0500
Labor Time: 0.8 hr.
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.