REVISION: SERVICE CALIBRATORS CORVETTE ROUGH,IDLE,SURGE,CEL. Chevrolet Corvette 1986

VEHICLES AFFECTED: 1986 Corvette

New service calibrations (Ref. called Mem-Cal in Shop Manual) have been released for the 1986 Corvette with the 5.7L TPI engine. These calibrators will address the following customer comments:

1. "Rough Idle" on both hot and cold engine - The idle speed is raised to 625 plus or minus 25 RPM with automatic transmission and 750 plus or minus 50 with manual transmission vehicles.

2. "Chuggle or Shudder" at low speeds - Torque converter clutch (TCC) engagement speed is raised to 65 k/ph (41 mph) with automatic transmission vehicles.

3. "Surge" at Road Load - This improvement is for automatic transmission vehicles only.

4. "Engine Overspeed" in lst gear - This improvement is for manual transmission vehicles only.

5. "Hesitation" on light acceleration with a hot engine.

6. "Service Engine Soon" lights - eliminates the following false codes:

A. Code 33 - Mass Airflow Sensor Voltage High

B. Code 34 - Mass Airflow Sensor Voltage Low

C. Code 4 3- Electronic Spark Control (ESC) this correction is for case iron head Corvettes only (VIN #119016 or earlier)

If normal engine diagnostics and repair do not correct the above conditions, it will be necessary to replace the calibrator in the ECM. Below is a listing of the new calibrators and their usages.

I. On Iron-Head Corvettes (VIN #119016 or earlier)

A. Manual Transmission - use 1227943 B. Automatic transmission with 2.59 (GMI) Axle - use 1227942 with 3.07 (G44) Axle - use 1227944

II. On Aluminum Head Corvettes (VIN #119016 or Later)

* A. Manual Transmission - use 1228473 B. Automatic Transmission with 2.59 (GMI) Axle - use 1228107 with 2.73 (GU2) 3.07 (G44) - use 1228109

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.