IDLE RISE BETWEEN SHIFTS (NEW CALIBRATION PROM)

SUBJECT: IDLE-RISE BETWEEN SHIFTS (NEW CALIBRATION-PROM)

VEHICLES AFFECTED: 1989-90 4.3L C/K TRUCKS WITH MANUAL TRANSMISSION (LESS THAN 8500# GVW)

CONDITION:

---------- Some owners of the above trucks equipped with manual transmissions may comment about a slight rise in engine idle speed when depressing the clutch to shift gears.

CORRECTION:

----------- To correct this condition a new service calibration PROM should be installed. The new calibration increases the rate at which Idle Air Control (IAC) counts are removed following a rapid closing of the throttle. Use the following VIN breakpoint and application charts to select proper PROM usage

VIN BREAKPOINTS (1990 MODEL YEAR):

L1512329 GMC OSHAWA (Plant Code 1) L1126446 CHEVROLET

LZ516573 GMC FORT WAYNE (Plant Code Z) LZ152371 CHEVROLET

LE512912 GMC PONTIAC EAST (Plant Code E) LE144515 CHEVROLET

APPLICATIONS: ALI, 1989 & 1990 BUILT PRIOR TO 1990 VIN BREAKPOINTS

SERVICE PROM BROADCAST YEAR SERIES TRANS EMISS PROM P/N ID CODE ---- ------ ----- ----- -------- ---- --------- 89-90 C/K M-5 (MG5) FED/ALT 16154687 4731 AWDM (NA5/NA6)

89-90 C10 M-4 (M20) FED/ALT 16154688 4741 AWDN (NA5/NA6)

89-90 K10 M-4 (M20) FED/ALT 16154689 4751 AWDP (NA5/NA6)

These PROMs will only function in service ECM (Electronic Control Module), P/N 1227747.

APPLICATIONS: ALL 1990 BUILT AFTER 1990 VIN BREAKPOINTS

SERVICE PROM BROADCAST YEAR SERIES TRANS EMISS PROM P/N ID CODE ---- ------ ----- ----- --------- ---- --------- 90 C/K M-5 (MG5) FED/ALT 16154690 4761 AWDR (NA5/NA6)

90 C/K M-4 (M20) FED/ALT 16154919 4921 AWDY (NA5/NA6)

These PROMs will only function in service ECM (Electronic Control Module), P/N 1614428

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.