K 1500 Truck 4WD V8-4.8L VIN V (1999)
PROM - Programmable Read Only Memory: All Technical Service Bulletins
Engine - Idle Shake in Drive, Park or Neutral
File In Section: 6E - Engine Fuel & Emission
Bulletin No.: 86-65-06
Date: November, 1998
Subject:
Engine Idle Shake in Drive, Park, or Neutral
(Replace Motor Mounts and/or Reflash Calibrations)
Models:
1999 Chevrolet Silverado and GMC Sierra Models
with 4.8L, 5.3L Engine (VINs V, T - RPOs LR4, LM7) and
Automatic Transmission (RPO M30)
Condition
Some owners of the above early production vehicles may comment on an engine idle shake (rough idle) with the transmission in Drive, Park, or Neutral
and the engine at normal operating temperature.
Cause
On some early production trucks, new stiffer motor mounts were developed to correct any concerns of an idle shake in Drive. These new motor mounts
improved the idle shake in Drive, however, the new mount created a Park/Neutral idle shake. Because of this, new engine calibrations were released to
correct the Park/Neutral idle speed.
Correction
A new motor mount has been developed to correct the condition of idle shake in Drive. On affected vehicles built within the following VIN breakpoints,
replace only the motor mounts. Refer to the 1999 Silverado and Sierra Service Information for engine mount replacement procedures. Use the part
number listed below.
For vehicles built prior to the following VIN breakpoints, replace both of the motor mounts and reflash the PCM with the appropriate calibration.
The new calibrations lower the engine idle speed 25 RPM from 600 RPM to 575 RPM at coolant temperatures above 68°C (154°F).
