ENGINE IDLE SHAKE IN DRIVE, PARK, OR NEUTRAL. GMC Truck GMC K Sierra

SUBJECT: ENGINE IDLE SHAKE IN DRIVE, PARK, OR NEUTRAL (REPLACE MOTOR MOUNTS AND/OR REFLASH CALIBRATIONS)

MODELS: 1999 CHEVROLET SILVERADO AND GMC SIERRA MODELS WITH 4.8L OR 5.3L ENGINE (VINS V, T - RPOS LR4, LM7) AND AUTOMATIC TRANSMISSION (RPO M30)

CONDITION:

SOME OWNERS OF THE ABOVE EARLY PRODUCTION VEHICLES MAY COMMENT ON AN ENGINE IDLE SHAKE (ROUGH IDLE) WITH THE TRANSMISSION IN DRIVE, PARK, OR NEUTRAL AND THE ENGINE AT NORMAL OPERATING TEMPERATURE.

CAUSE:

ON SOME EARLY PRODUCTION TRUCKS, NEW STIFFER MOTOR MOUNTS WERE DEVELOPED TO CORRECT ANY CONCERNS OF AN IDLE SHAKE IN DRIVE. THESE NEW MOTOR MOUNTS IMPROVED THE IDLE SHAKE IN DRIVE, HOWEVER, THE NEW MOUNT CREATED A PARK/NEUTRAL IDLE SHAKE. BECAUSE OF THIS, NEW ENGINE CALIBRATIONS WERE RELEASED TO CORRECT THE PARK/NEUTRAL IDLE SPEED.

CORRECTION:

A NEW MOTOR MOUNT HAS BEEN DEVELOPED TO CORRECT THE CONDITION OF IDLE SHAKE IN DRIVE. ON AFFECTED VEHICLES BUILT WITHIN THE FOLLOWING VIN BREAKPOINTS, REPLACE ONLY THE MOTOR MOUNTS. REFER TO THE 1999 SILVERADO AND SIERRA SERVICE INFORMATION FOR ENGINE MOUNT REPLACEMENT PROCEDURES. USE THE PART NUMBER LISTED BELOW.

PLANT DIVISION VIN BREAKPOINT ----- -------- -------------- PONTIAC-EAST CHEVROLET XE100034 - XE104645 GMC XE500028 - XE501856

FOR VEHICLES BUILT PRIOR TO THE FOLLOWING VIN BREAKPOINTS, REPLACE BOTH OF THE MOTOR MOUNTS AND REFLASH THE PCM WITH THE APPROPRIATE CALIBRATION.

PLANT DIVISION VIN BREAKPOINT ----- -------- -------------- OSHAWA CHEVROLET X1105183 GMC X1500767

THE NEW CALIBRATIONS LOWER THE ENGINE IDLE SPEED 25 RPM FROM 600 RPM TO 575 RPM AT COOLANT TEMPERATURES ABOVE 68 DEGREES C (154 DEGREES F).

CALIBRATION P/N ENGINE FUEL/EMISSIONS --------------- ------ -------------- 16263835 LR4 NF2-NN8 (UNLEADED/FED. + CANADA) 16263836 LR4 NN8 (UNLEADED/NON-EUROPEAN EXPORT) 16263837 LR4 NC1 (UNLEADED/CALIFORNIA LEV) 16263838 LM7 NF2-NN8 (UNLEADED/FED. + CANADA) 16263839 LM7 NN8 (UNLEADED/NON-EUROPEAN EXPORT) 16263840 LM7 NC1 (UNLEADED/CALIFORNIA LEV) 16263841 LM7 NM2 (LEADED/ALL EXPORT)

IMPORTANT: THE CALIBRATIONS LISTED ARE FLASH CALIBRATIONS AND ARE NOT AVAILABLE FROM GMSPO. THESE CALIBRATIONS ARE AVAILABLE ON 1998 TECHLINE CD ROM DISC 18 AND LATER.

REPLACING THE ENGINE MOUNTS ALONG WITH REFLASHING THE NEW CALIBRATIONS SHOULD ADDRESS THE IDLE SHAKE CONDITION.

PARTS INFORMATION:

P/N DESCRIPTION QTY --- ----------- --- 15041508 MOUNT ASM - ENGINE FRAME SIDE 2

PARTS ARE EXPECTED TO BE AVAILABLE 10-26-98 FROM GMSPO.

WARRANTY INFORMATION:

FOR VEHICLES REPAIRED UNDER WARRANTY, USE:

LABOR OPERATION DESCRIPTION LABOR TIME --------- ----------- ---------- J1507 MOUNT, ENGINE USE PUBLISHED LABOR - REPLACE (BOTH) OPERATION TIME

J6355 PROM - REPROGRAMMING USE PUBLISHED LABOR (ON CAR) OPERATION TIME

FIGURES: 00 ATTACHMENTS: 00

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.