COLD ROUGH IDLE AND DETONATION (NEW CALIBRATION)

SUBJECT: COLD ROUGH IDLE AND DETONATION (NEW CALIBRATION)

VEHICLES AFFECTED: 1993 "M" VANS WITH 4.3L V6 ENGINE (RPO LB4)

CONDITION:

Some owners of 1993 model year "M" vans equipped with LB4 4.3L V6 VIN Z (NOT L35 VIN W may report a rough idle or shake during engine warmup and/or detonation during normal engine operation. Vehicles built before the following VIN breakpoints are affected.

CHEVROLET: PB177872 GMC: PB531344

CAUSE:

Idle Shake Engine idle speed causing undesirable body vibration during warmup. Detonation ESC system retard rate may be too slow.

CORRECTION:

A calibration has been developed to minimize the time the engine operates at the speed where the vibration can occur. The calibration also contains enhancements to the ESC system that will lessen the possibility of detonation.

APPLICATION OLD PROM OLD OLD PROM NEW PROM NEW NEW PROM AXLE KIT B/C ID KIT B/C ID ------------- -------- --- -------- -------- ---- --------

FED 3.23/3.42 16179608 BBMY 9411 16192233 BFMY 2235 FED 3.73 16179613 BBMZ 9421 16192237 BFMZ 2245

CALIF 3.23/3.42 16179662 BBNC 9451 16192242 BFNA 2255 CALIF 3.73 16179668 BBND 9461 16192246 BFNB 2265

For vehicles repaired under warranty use:

Labour Time: 0.6 Hours

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.