IDLE RISE BETWEEN SHIFTS (NEW CALIBRATION PROM)

Subject: IDLE RISE BETWEEN SHIFTS

Model and Year: 1989-90 C/K TRUCKS WITH MANUAL TRANSMISSION AND 4.3L (VIN CODE Z) ENGINE

TO: ALL CHEVROLET DEALERS

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 the proper PROM usage.

VIN BREAKPOINTS: 1990 Model Year

L1126446 OSHAWA (Plant Code 1)

LZ152371 FORT WAYNE (Plant Code Z)

LE144515 PONTIAC EAST (Plant Code E)

APPLICATIONS: ALL 1989 AND 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 C/K M-5(MG5) CALIF 16155647 5691 AWJR (NB2) 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)

SERVICE PROM BROADCAST YEAR SERIES TRANS EMISS PROM P/N ID CODE --- ------ ----- ----- --------- ---- --------- C/K 20 89-90 C/K M-4(M20) CALIF 16155648 5701 AWJS (NB2)

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

APPLICATIONS: ALL 1990 BUILT AFTER 1990 VIN BREAKPOINTS

90 C/K M-5(MG5) FED/ALT 16154690 4761 AWDR (NA5/NA6) 90 C/K M-5(MG5) CALIF 16155650 5721 AWJU (N B2) 9 0 C/K M-4(M20) FED/ALT 16154919 4921 AWDY (NA5/NA6) 90 C/K M-4(M20) CALIF 16155649 5711 AWJT (NB2)

These PROMs will only function in service ECM (Electronic Control Module), P/N 16144288.

Parts are currently available from GMSPO.

Labor Operation Number: T0500

Labor Time: .6 Hrs

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.