DRIVEABILITY/EGR SURGE OR HARD 3-2 DOWNSHIFT

DRIVEABILITY - EGR SURGE AND ABRUPT 3-2 DOWNSHIFT

VEHICLES AFFECTED 1988 J AND N CARS WITH 2.0L TURBO ----------------- ENGINE (VIN CODE M) AND AUTOMATIC TRANSMISSION

Some early built 1988 J and N cars with the 2.0L turbo engine may demonstrate one or both of the following driveability conditions:

1. Exhaust Gas Recirculation (EGR) Induced Surge

Light surge at road load driving conditions (approximately 65 km/hr.) with a warmed-up engine. Disconnecting the EGR valve and plugging the vacuum line will verify EGR induced surge.

2. Abrupt 3-2 Downshift

During a passing maneuver in the 65-90 km/hr. speed range, a potentially harsh 3-2 downshift prior to normal torque converter clutch (TCC) unlock may occur. Other automatic transmission conditions (if present) should be corrected prior to any final verification of the above condition.

These conditions can be repaired by changing the ECM calibration PROM. Using a scanner, the original PROM I.D. can be verified.

PROM I.D. REPLACEMENT PROM ---------- ----------------- 4262 16120036

Only vehicles showing the above "PROM I.D." will need the replacement PROM.

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.