HESITATION, ROUGH IDLE & VIB. DIAG./REPL. ECM/TBI AND DAMPER

SUBJECT: HESITATION, ROUGH IDLE AND VIBRATION (DIAGNOS/REPLACE ECM/TBI AND DAMPER)

VEHICLES AFFECTED: 1992 "M" MODELS WITH 1.3L ENGINE (VIN 9, RPO L72) AND AUTOMATIC TRANSAXLE

CONDITION:

--------- Some owners of 1992 Geo Metros with 1.3L engine (VIN 9, RPO L72) and automatic transaxle may experience engine hesitation, extreme rough idle and vibration at certain engine coolant temperatures.

CAUSE:

----- ECM and TBI calibration, along with steering wheel damping.

CORRECTION:

---------- If any of the subject conditions are found, they may be corrected by new engine calibration and TBI replacement to improve engine operation and installation of a steering mass damper for rough idle and vibration above 60 degrees Celsius (coolant temperature) after warm up.

Use the following procedure:

1. Record customer comment, vehicle symptoms and the coolant temperature when condition occurs.

2. Inspect spark plugs for proper type, condition and gap. Ensure that all high tension lead resistances are within specifications.

3. Check and adjust ignition timing and idle speed to specification (Section 6E2 of the Service Manual).

4. Check throttle position sensor adjustment (Service Manual Section 6E2). Refer to Figure 3 of this bulletin for revised specifications.

5. Inspect all vacuum hose connections for proper routing.

6. Check fuel pressure (Section 6E2-Chart A-7A,B,C of the Service Manual).

7. If the condition still exists after performing the above steps, follow the appropriate section of the table on page 2.

SYMPTOM COOLANT TEMPERATURE CORRECTION ------- ------------------- Unacceptable steering 60 deg. Celsius or above Remove I/P bracket wheel vibration. after warm-up phase Install steering mass damper kit.

Hesitation on acceleration, Below 20 deg. Celsius Replace ECM and rough idle, and vibration. - after starting Trottle Body Assembly (Note 1)

Rough idle and vibration. 20 to 60 deg. Celsius Replace Throttle Body - warm-up phase Assembly. (Note 1)

Note 1: - If steering wheel vibration remains , remove I/P bracket (Fig. 1) and install the steering mass damper kit (Fig. 2).

o To access the Instrument Panel Bracket (I/P bracket), remove the centre gear shift console assembly, (See Fig. 1).

o The steering wheel has to be removed (refer to Service Manual Section 3F 1 -4), to separate the horn contact assembly from the steering wheel assembly. This will allow the replacement of the steering mass damper. (See Fig. 2).

o Refer to Figure 3., revision to Service Manual "Throttle Position Sensor Output Check". Make the necessary corrections in Service Manual (page 6E2-C2-15).

PARTS INFORMATION:

Auto. Transaxle --------------- ECM 96067698

TBI 96067865

TBI Base Gasket 96067863

Steering Mass Damper 96067645

NOTE: Adjustment information after ECM and TBI replacement.

o Ensure proper engine idle speed (850 + 50 RPM), Service Manual Section 6E2-C2-8

o Using your Tech 1, Submenu Misc. Test, Parameter "ISC Cal Air", ensure the ISC Duty is 15 5% with :

a) Headlights "ON"

b) Gear Selector in "PARK"

o Refer to Fig. 4 for location of ISC Duty adjustment screw (which is the idle speed screw).

For vehicles repaired under warranty use:

Description Labour Operation: Labour Time: ----------- ---------------- ----------- Replace ECM and TBI T8200 1.3 Hours

Replace TBI Only T8201 1.1 Hours

Remove I/P Bracket and install T8202 0.5 Hours Steering Damper

Replace TBI, remove I/P Bracket T8203 1.5 Hours and install Steering Damper

Replace ECM / TBI, remove I/P T8204 1.7 Hours Bracket and install Steering Damper

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.