IDLE RISE BETWEEN SHIFTS (NEW CALIBRATION PROM). GMC Truck GMC C Pickup

SUBJECT: IDLE RISE BETWEEN SHIFTS (NEW CALIBRATION PROM)

MODELS: 1989-90 4.3L C/K TRUCKS WITH MANUAL TRANSMISSION (5LM60, HM117) AND GVW LESS THAN 8500#

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

SERVICE PARTS INFORMATION

APPLICATIONS: These PROMs will only function in service ECM (Electronic Control Module), P/N 1227747. increases the rate at which Idle Air Control (IAC) counts are removed following a rapid closing of the throttle.

To determine correct service PROM usage, verify the part number of the ECM currently installed in the vehicle, and follow the appropriate chart.

Series Trans. Emiss. Service PROM ID Broadcast PROM P/N Code ----- --------- ---------------- -------- ----- ----------- C/K M-5 (MG5) FED/ALT (NA5/NA6) 16154687 4731 AWDM

C/K M-5 (MG5) CALIF (NB2) 16155647 5691 AWJR

C 1 M-4 (M20) FED/ALT (NA5/NA6) 16154688 4741 AWDN

K 1 M-4 (M20) FED/ALT (NA5/NA6) 16154689 4751 AWDP C/K 2

C/K M-4 (M20) CALIF (NB2) 16155648 5701 AWJS

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

Series Trans. Emiss. Service PROM ID Broadcast PROM P/N Code ------- -------- ---------------- -------- ---- ---------- C/K M-5 (MG5) FED/ALT (NA5/NA6) 16154690 4761 AWDR C/K M-5 (MG5) CALIF (NB2) 16155650 5721 AWJU C/K M-4 (M20) FED/ALT (NA5/NA6) 16154919 4921 AWDY C/K M-4 (M20) CALIF (NB2) 16155649 5711 AWJT

Parts are currently available through GMSPO.

WARRANTY INFORMATION

Labor Operation: T0500

Labor Time: .6 Hrs

NOTE. Labor Operation is coded to base vehicle coverage in the warranty system.

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.