ROUGH IDLE OR POOR PERFORMANCE (CHECK INTAKE PLENUM RUNNERS)

1985-86 6000 AND FIREBIRD MODELS WITH 2.8L MPFI V-6 ENGINES RPO CODES LB6 & LB8, VIN CODES W & S

A condition exists whereby one or more ports of the inlet plenum can be partially or completely blocked with casting flash. The condition can cause rough idle, rough engine operation, and/or poor performance. The casting flash, if present, can be found approximately two (2) inches in from the plenum mounting surface by probing with feeler stock. The casting flash may not be visible to the eye (see figure 1).

To correct this condition, replace the inlet plenum using applicable labor operations and times as publishes.

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.