STALL,TIP-IN HES. AND/OR STORED ENGINE CODES (PROMS)

MODELS AFFECTED: 1987 CIMARRONS

This bulletin supersedes bulletin T-90-4 to include new part numbers for vehicles with manual transmission. Bulletin T-90-4 should be discarded.

Some 1987 Cimarrons may experience one or more of the following conditions:

Engine stall or sag on cold start. Engine stall on deceleration. Tip-in hesitation on acceleration. Check engine light with stored codes 23, 35, 33, or 34. Engine speed flare during a declutch operation with a manual transmission equipped vehicle.

1. Perform diagnostic procedures per Section 6E of the Service Information Manual and correct any faults except for codes 33, 34, 23, or 25. If the diagnostics indicate the Mass Air Flow (MAF) is to be replaced or a code 33 or 34 is present AND a code 23 or 25 is present, DO NOT REPLACE THE MAF SENSOR! Proceed to step 2 below. PROCEED DIRECTLY TO STEP 3 ONLY IF A CODE 23 OR 25 IS NOT PRESENT.

2. If a code 23 or 25 is stored, perform the model year diagnostics for the Manifold Air Temperature (MAT) sensor. If the diagnostics indicate that the MAT is faulty and replacement is required, replace the combination MAT/MAF sensor. Proceed to step 3.

3. Install a new MEM-CAL into the Engine Control Module (ECM) per the instructions below. The new MEM-CAL is available from GMSPO. See the following service part number chart. Install the identification label package to the ECM access door and to the left shock tower per label kit, P/N 10154725, instructions.

IMPORTANT: The new MEM-CAL to be installed does not need or use the existing MAF signal, however, it does need and use the MAT signal.

A. Pull the fuel pump in-line fuse or disconnect the battery and leave it disconnected for at least 10 minutes.

B. Remove the MAF relay and discard. Tape up connector to prevent water intrusion.

C. Remove current MEM-CAL and install a new service MEM-CAL.

D. Restore the battery power and place air conditioning controls in the "off" position. transaxle to "drive" for automatics or "neutral" for manuals.

F. Allow the engine to run until the engine cooling fan has cycled once, or a maximum of ten minutes.

G. Turn the ignition key to the "off" position for at least five seconds.

H. Start the engine and shift the transaxle to "drive" for automatics or "neutral" for manuals.

I. Allow engine to run for at least five minutes.

After a MEM-CAL replacement, the 1988 2.8L speed density service diagnostics must be used for driveability and emissions diagnostics. For additional information, call CAD-STAR. For warranty purposes use Labor Operation J5 670 at .4 hour for MAF/MAT replacement and Labor Operation T1492 at .9 hour for MEM-CAL change.

MEM-CAL SELECTION CHART-SERVICE PART NUMBERS

IMPORTANT: MEM-CAL MUST BE ORDERED WITH LABEL KIT, P/N 10154725

Model Emission MEM-CAL Scanner Broadcast Year Transmission Configuration P/N I.D. Code ---- ------------- ------------- --- ---- ---- 1987 Automatic 3-Speed Fed. 16140342 0381 ASMN 1987 Manual 5-Speed Fed. 16148227 8261 ATZA 1987 Automatic 3-Speed Cal. 16140343 0391 ASMP 1987 Manual 5-Speed Cal. 16148228 8271 ATZB

Parts are currently available from GMSPO.

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.