ENGINE STALLS ON COAST DOWN (CLEAN CARBON DEPOSITS)

SUBJECT: ENGINE STALLING ON COAST DOWN (PERFORM DIAGNOSIS AND CLEAN CARBON DEPOSITS)

VEHICLES AFFECTED: 1990-91 C, E, K

This bulletin has been revised to include updated part number, warranty, and repair procedure information. The repair procedure now includes installing an updated PCM PROM if required and revised idle learn procedures. This bulletin replaces 91-649-103 which should be discarded.

Some 1990-1991 DeVilles, Fleetwoods, Eldorados, and Sevilles may experience a stall on coast down with an immediate restart. This condition may be accompanied by an ECM code E22, E26, E32, E55, E70, or E85. This may be caused by an erratic signal from the Throttle Position Sensor (TPS).

To repair this condition use the following procedure:

1. Perform trouble code diagnosis. Refer to Section 8Dl of the appropriate Service Information Manual.

2. Clean engine grounds per Product Service Bulletin 90-645-107.

3. Inspect the ISC harness behind the generator and the TPS wires for chafing, cuts, or poor connections and repair if necessary.

4. Check brake switch and throttle switch operation using vehicle on-board diagnostics.

5. Clean carbon deposits from the throttle blades and bores using a soft bristle brush (i.e., toothbrush) and GM top engine cleaner, P/N 993026, or AC-Delco carburetor tune-up conditioner, P/N X66-P, or equivalent.

IMPORTANT: Do not use any solvent that contains methyl ethyl ketone.

6. Visually inspect the TPS. If the TPS is the old style, replace it with part number 17112609. Refer to Section 6E-C2 of the appropriate Service Information Manual.

7. On 1991 vehicles, check the PCM PROM I.D. using on-board diagnostics. If the PROM I.D. does not match the chart below, replace the PROM with the indicated part number.

Prod. Serv. Service Emission PROM PROM Broadcast Service VIN Vehicle System I.D. I.D. Code P/N Breakpoint -------- ------ ---- ----- ------- ------- ---------- C Fed. 365 384 AYFP 16164699 302143 60 Special Fed. 368 387 AYFT 16164702 302146 C-Touring Fed. 372 383 AYFH 16164692 301444 E Fed. 1024 1041 AYKM 16165502 614118 ETC Fed. 1028 1043 AYKP 16165511 614124 K Fed. 1024 1041 AYKM 16165502 821255 STS Fed. 1028 1043 AYKP 16165511 821269

8. Verify base timing is at 10 degrees BTDC or 6 degrees if regular unleaded fuel is being used.

NOTE: The generator must be disabled when performing steps 8 and 9. To disable the generator on a DeVille or Fleetwood ground the green generator disable lead. The generator is automatically disabled on an Eldorado or Seville by the ECM during the ISC override.

9. Adjust Minimum Air per Section 6E-C2 of the appropriate Service Information Manual making sure that the ISC harness is disconnected when the ISC is fully retracted.

10. Adjust TPS per Section 6E-C2 of the appropriate Service Information Manual.

NOTE: On DeVilles and Fleetwoods, TPS jumper harness tool J-38490 and a DVM must be used to properly set the TPS.

11. Disconnect battery and clear codes.

12. Perform TPS learn: o Turn ignition on (engine not running). o Enter diagnostics. o Turn ignition off. o Wait a minimum of 20 seconds. o Turn ignition on (engine not running). o Re-enter diagnostics. o Turn ignition off. o Wait a minimum of 20 seconds. o Turn ignition on (engine not running). o Re-enter diagnostics. o Turn ignition off. o Wait a minimum of 20 seconds.

NOTE: Do not touch the accelerator or brake pedal during the TPS learn procedure.

13. Perform idle learn: o Start the engine. o On a 1990 vehicle allow the vehicle to idle continuously for 18 minutes. o On a 1991 vehicle allow the vehicle to idle continuously for 13 minutes. o Place the transmission in drive with the brakes applied. o Place the vehicle climate control in the OFF position, and allow the engine to remain at idle for at least one minute. o Make sure the outside air temperature reading is at least 50 degrees F. o Place the vehicle climate control in the AUTO position, verify A/C clutch engagement, and allow the engine to remain at idle for at least one minute. o Place the transmission in park and turn ignition off.

IMPORTANT: Because of the load differences on the engine with A/C on versus A/C off, learning must be allowed under both conditions.

Parts are currently available from CANSPO.

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.