COLD START/STALL HESITATION NEW ECM/REPLACE T/B AIR VALVE

Subject: COLD START/STALL HESITATION

Model and Year: 1990-92 GEO PRIZM GSI WITH 1.6L ENGINE

Condition: Some owners of 1990-92 (prior to VIN breakpoint #NZ035000) Prizm GSI vehicles with the 1.6L engine (VIN 5) may comment on a hesitation, loss of power, or stall condition, while the engine is cold and a quick acceleration is attempted.

Correction: For vehicles exhibiting this condition, replace the Electronic Control Module (ECM) located in the center of the instrument panel behind the console.

P/N 94852501 replaces P/N 94851354 for federal emissions and P/N 94852500 replaces P/N 94851355 for California emissions.

After replacing the ECM, the minimum idle speed adjustment should be checked and adjusted, as necessary, according to the Service Manual procedure.

On 1991 model year vehicles built between VIN MZ053796 and MZO86198, the Valve, Throttle Body Auxiliary Air P/N 94845502, should also be replaced in addition to the ECM. The auxiliary air valve is part of the fuel injection throttle body assembly and is shown on the attached illustration as item #3.

Normal Service Manual procedures should be followed for the above part replacements.

Part Information:

Parts are currently available from GMSPO.

Labor Operation and Time:

T1861 - 1991 Vehicles (VIN MZ053796 through MZ086198) 1.5 Hr. T1862 - All Others (1990 through 1992) 1.0 Hr.

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.