ENG. MAY INTERMITTENTLY STALL CHECK FOR RESIDUE ON THROTTLE

1985-87 6000 AND FIREBIRD MODELS EQUIPPED WITH 2.8L V6 PFI ENGINES

"This bulletin supersedes bulletin 87-6(Gasoline)-32, dated 4/87, to correct Step #9 and the warranty information. Please discard 87-6(Gasoline)-32."

Some 1985-87 vehicles equipped with 2.8L V-6 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 Car Lines Minimum Idle Speed Specification* ----- ---------- --------------------------------- 1985-86 6000, Firebird 550 +/- 50 RPM in drive (auto. trans.) 650 +/- 50 RPM in neutral (man. trans.) 1987 Firebird 550 +/- 50 RPM in drive (auto. trans.) 650 +/- 50 RPM in neutral (man. trans.) 1987 6000 550 +/- 50 RPM in drive (auto. trans.) 675 +/- 50 RPM in neutral (man. trans.) *Engine should be at normal operating temperature.

3. Remove the negative battery terminal.

4. Remove mass airflow duct at throttle body.

5. Cover TPS and IACV to protect from overspray.

6. Clean the throttle body bore in the area behind the throttle body.Use a shop towel with GM Top Engine Cleaner, P/N 1052626, or AC-Delco Carburetor Tune-Up Conditioner, P/N X66-A, or equivalent that doesn't contain methyl ethyl ketone. It should be noted that what appears to be a small amount of accumulation can be enough to limit air flow.

7. Install mass airflow duct.

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

1987 Model Year VIN Breakpoints

Carline VIN

6000 9244354 T244412

Firebird N224963 L215142

9. Recheck minimum idle speed on 1985-86 vehicles, and 1987 vehicles 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 reconnect IAC electrical connector.

9. Adjust TPS to 0.55 +/- 0.08 volts.

Warranty Information:

Labor Operation: T1205 Labor Time : .5 Hour 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.