ENG. MAY INTERMITTENTLY STALL CHECK FOR RESIDUE ON THROTTLE

MODELS AFFECTED: 1985 SKYLARKS AND 1987 CENTURYS EQUIPPED WITH THE LB6 2.8L MPFI V6 ENGINE (VIN CODE W)

NOTICE: This bulletin supersedes bulletin 87-6E-15 to correct Step 9 and the Warranty infomation. Please discard 87-6E-15

Some of the subject vehicles equipped with 2.8L MPFI V6 engines may experience a stall after start with a warmed up engine or a stall during deceleration.

This condition may be caused by residue accumulating inside the throttle body bore behind the throttle plate and limiting air flow past the throttle plate in the idle position.

To diagnose this condition, perform the following steps:

1. Measure minimum idle speed using procedures defined in Section 6E3 of the Service Manual which follow:

a. Ground diagnostic "test" terminal. b. Turn ignition "ON", but do not start engine. c. Wait 30 seconds and disconnect IAC electrical connector. d. Remove ground from diagnostic "test" terminal, start engine, and allow system to go to "closed loop". e. Note idle RPM in "drive". f. Turn ignition "OFF" and reconnect IAC electrical connector.

2.If the minimum idle speed is less than what is specified in Chart I, proceed to Step 3. Otherwise, perform activities defined in the Service Manual under Section 6E3, Section B - Rough, Unstable, Or Incorrect Idle, Stalling.

CHART I - MINIMUM IDLE SPEED Model Year Carline Minimum Idle Sveed Specification *

1985 Skylark 550 + or - 50 RPM in drive (auto. trans.) 650 + or - 50 RPM in neutral (manual trans..)

1987 Century 550 + or - 50 RPM in drive (auto. trarls.)

* Engine should be at normal operating temperature.

3. Remove the negative battery terminal.

4. Remove mass air flow duct at throttle body.

5. Cover TPS and IAC to protect from overspray.

6. Clean the throttle body bore in the area behind the throttle plate. Use a shop towel with GM Top Engine Cleaner, Part Number 1052626, or AC-Delco Carburetor Tune-Up Conditioner, Part Number X66-A, or equivalent that doesn't contain methyl ethyl ketone.

It should be noted that what appears to be a small amount of residue accumulation can be enough to limit air flow.

7. install mass air flow duct.

8. 1987 model year Centurys built after the following VIN breakpoints will not require rechecking and resetting of-minimum idle speed.

1987 Model Year VIN BreakDoints

Plant VIN

Doraville D442400 Oklahoma City 6424153 Tarrytown T429618

9. Recheck minimum idle speed on 1985 Skylarks and 1987 Centurys built prior to the above VIN breakpoints and adjust, if necessary, to specifications defined in Step 2. Use the following procedure to recheck and adjust:

a. Ground diagnostic "test" terminal. b. Turn ignition "ON", but do not start engine. c. Wait 30 seconds and disconnect IAC electrical connector. d. Remove ground from diagnostic "test" terminal, start engine, and allow system to go to "closed loop". e. Note idle RPM in "drive" and adjust to specification (idle stop screw plug must be removed to gain access to idle stop screw). f. Turn ignition "OFF" and reccnnect IAC electrical connector. g. Adjust TPS to 0.55 +/- 0.08 volts.

Warranty Information

Labor Operation Number: T1205 Labor Time: 0.5 Hours Trouble Code: 92

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.