Engine - Surge or Chuggle On Decel/Rough Idle
Number: 91-516-6ESection: 6E
Date: OCT. 1992
Corporate Bulletin No.: 036516R
ASE No.: A1, A8
Subject:
SURGE OR CHUGGLE ON DECEL AND/OR ROUGH IDLE
Model and Year:
1990-91 S/T TRUCKS WITH 4.3L ENGINE AND 5LM60 MANUAL TRANSMISSION
THIS BULLETIN CANCELS AND SUPERSEDES DEALER SERVICE BULLETIN NO. 90-425-6E, DATED MAY 1991. THE 1991 MODEL YEAR HAS BEEN ADDED AS WELL AS CAUSE AND CORRECTION REVISED. ALL COPIES OF 90-425-6E SHOULD BE DISCARDED.
CONDITION:
Owners of some 1990-1991 S/T trucks equipped with 5-speed manual transmissions may comment about one or more of the following conditions:
- An engine deceleration surge or chuggle at light throttle cruise or coast
- Rough idle, cold or hot
CAUSE:
These conditions are related to EGR (Exhaust Gas Recirculation), fuel and spark control calibrations, and idle speed.
CORRECTION:
A new service calibration has been developed which contains updates to EGR, Fuel and Spark Control and increases idle speed to 700 rpm from 600 rpm. To correct any of the above conditions install a new prom (Programmable Read Only Memory) using the application chart.
NOTE:
1990 model year trucks require ECM (Engine Control Module) P/N 16144288 in order to use the new prom. 1991 model year trucks should already have this engine controller. Also note that the new calibration is nationwide, replacing both federal and California emission original production calibrations.
Part Availability:
Parts are currently available from GMSPO.
Warranty Information:
Labor Operation: T0500
Labor Time: 0.8 Hr.