DELAYED AND HARSH UPSHIFTS REVISED THROTTLE BODY ASSY.

MODELS AFFECTED: 1987 CENTURYS WITH 2.8L MPFI V6 ENGINES (LB6) AND AUTOMATIC TRANSAXLES

NOTICE- This bulletin is revised to include inspection, replacement, and adjustment procedures. File Group is also changed. Discard the original bulletin 87-7125-2 and replace with this bulletin.

Some early built 1987 Centurys with 2.8L V6 engines (VIN Code W) and THM 125C (MD9) or 440-T4 (ME9) automatic transaxles may exhibit delayed and or harsh upshifts, and in some cases a reduction in detent downshift availability.

After the condition has been verified, inspect the Throttle Valve (TV) cable for proper operation and adjustment. Follow the TV cable adjustment procedures contained in the Buick Chassis Service Manual, Section 7A1. If the TV system is operating properly and the condition still exists, it may be caused by insufficient travel of the throttle lever on the throttle body assembly.

Inspect the throttle lever for an identification hole in the location shown in the Illustration. If the lever has a hole, continue following the diagnosis covered in Automatic Transaxle section of the Service Manual. If the lever does not have a hole in it, at the location shown, install a new throttle body with a revised throttle lever. Throttle Body Service Kit as follows:

1987 Century With 2.8L MPFI (LB6) 17111886

NOTE: The Service Throttle Body Kit includes only the core throttle body. It does not include the following parts, which are available separately:

- Coolant Cover, ORing and attaching screws - Idle Air Control Valve, Housing and attaching screws - Throttle Position Sensor and attaching screws

These items can be transferred from the original throttle body assembly.

Follow the throttle body removal and installation procedures covered in the "Driveability and Emissions-Port Fuel Injection Section" 6E3 of the Service Manual. After installing the replacement throttle body, preset the throttle stop screw as follows:

- Back throttle stop screw out until it breaks contact with the throttle lever. Turn screw in to lightly contact lever, then 1 3/4 additional turns. Final minimum idle speed adjustment should be performed following the procedure below:

a. Ground diagnostic "test" terminal. b. Turn ionition "ON", but do not start engine. C. Wait 36 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. g. Adjust TPS to 0.55 +/- 0.08 volts.

- Adjust minimum idle speed to 550 +/- 50 RPM.

- Adjust TPS to 0.55 volts +/- 0.1 volts (0.45 to 0.65 volts).

WARRANTY INFORMATION Labor Operation Number: T1206 Labor Time: 0.9 Hours Trouble Code: 99

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.