ENG. HI. IDLE/FLARE WHEN SHIFTING GEARS. GMC Truck Jimmy

SUBJECT: ENGINE HIGH IDLE/FLARE WHEN SHIFTING GEARS (PERFORM FLASH CALIBRATION)

MODELS: 1998 CHEVROLET AND GMC S/T AND C/K MODELS WITH 4.3L ENGINE (VINS X, W - RPOS LF6, L35) AND MANUAL TRANSMISSION (RPOS - MG5, M50)

CONDITION:

SOME OWNERS MAY REPORT THAT THE ENGINE EXHIBITS A HIGH IDLE OR FLARE WHEN SHIFTING GEARS OR DISENGAGING THE CLUTCH SUCH AS WHEN SLOWING DOWN OR STOPPING.

CAUSE:

IF FOLLOWING STEPS 1,2 AND 3 OF STRATEGY BASED DIAGNOSTICS DID NOT REVEAL THE CAUSE, HIGH IDLE OR ENGINE FLARE MAY BE THE RESULT OF ADDITIONAL IDLE AIR CONTROL (IAC) AIR THAT IS LEARNED INTO THE STALL SAVER CALIBRATION.

VEHICLE OPERATION AT LOW ROAD SPEEDS 16-24 KM/H (10-15 MPH), IN A HIGH GEAR (5TH), CAUSES THE ENGINE TO LUG DOWN BELOW THE STALL SAVER THRESHOLD. THE OFF IDLE STALL SAVER CALIBRATION FOR THESE ENGINES IS APPROXIMATELY 500 RPM.

THIS SITUATION CAN BE EXPERIENCED DURING CITY DRIVING MANEUVERS, ESPECIALLY IN HILLY TERRAIN, WHEN THE DRIVER DOES NOT DOWNSHIFT THE TRANSMISSION AND FORCES THE ENGINE RPM UNDER THE STALL SAVER THRESHOLD.

DURING THIS CONDITION, THE IAC OPENS TO A CALIBRATED LEVEL IN AN ATTEMPT TO RAISE THE ENGINE RPM ABOVE THE STALL SAVER THRESHOLD. THIS LEVEL OF IAC AIRFLOW WILL CAUSE IDLE FLARE IF THE VEHICLE IS DRIVEN OUT OF THE LUGGING CONDITION (IE: DOWNSHIFTING) WITHOUT FIRST COMING TO AN IDLE. IDLING FIRST WOULD ALLOW THE ADDITIONAL IDLE AIR TO BE LEARNED BACK TO A NORMAL LEVEL.

THE NEW CALIBRATIONS REDUCE THE NUMBER OF STALL SAVER COUNTS THAT CAN BE LEARNED IN.

CORRECTION:

REFER TO THE TABLE BELOW FOR THE APPLICABLE CALIBRATION CHANGE. PERFORM PROGRAMMING PER THE LATEST TECHLINE INFORMATION FOR PROGRAMMING PROCEDURES.

OLD P/N NEW P/N APPLICATION 16267614 09350941 C/K WITH L35 + NN8 + MG5 16267615 09350945 C/K WITH L35 + MG5 16267656 16249448 S/T WITH L35 + NM8 + M50 16267658 16249450 S/T WITH L35 + NA7 + M50 16267660 16249452 S/T WITH L35 + NF2/NB6 + M50 16267662 16249554 S/T WITH L35 + NN8 + M50 16267664 16249556 S/T WITH LF6 + NF2/NB6 + M50

IMPORTANT: THE CALIBRATIONS LISTED ARE FLASH CALIBRATIONS AND ARE NOT AVAILABLE FROM GMSPO. THEY ARE AVAILABLE ON 1997 TECHLINE CD DISC 22 AND LATER.

WARRANTY INFORMATION FOR VEHICLES REPAIRED UNDER WARRANTY, USE:

LABOR OP LABOR TIME J6355 USE PUBLISHED LABOR 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.