ENG. HIGH IDLE/FLARE WHEN SHIFTING GEARS. GMC Truck Sonoma Pickup

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

MODELS: 1996-97 CHEVROLET AND GMC S/T MODELS WITH 4.3L ENGINE (VINS W, X - RPOS L35, LF6) AND MANUAL TRANSMISSION (RPO 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 THE STRATEGY BASED DIAGNOSTICS DID NOT REVEAL A 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 MAY BE EXPERIENCED DURING CITY DRIVING MANEUVERS, ESPECIALLY IN HILLY TERRAIN, WHEN THE DRIVER DOES NOT DOWNSHIFT THE TRANSMISSION OR DEPRESS THE CLUTCH 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 WILL CAUSE IDLE FLARE IF THE VEHICLE IS DRIVEN OUT OF THE LUGGING CONDITION (IE: DOWNSHIFTING OR DEPRESSING THE CLUTCH) WITHOUT FIRST COMING TO AN IDLE. IDLING FIRST WOULD ALLOW THE ADDITIONAL IDLE AIR TO BE LEARNED BACK TO A NORMAL LEVEL.

CORRECTION:

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

THE NEW CALIBRATIONS REDUCE THE NUMBER OF STALL SAVER COUNTS THAT CAN BE LEARNED WHILE LUGGING THE ENGINE. IN ADDITION, THESE NEW CALIBRATIONS MINIMIZE TURNING ON THE MIL LAMP DUE TO TEMPORARY OVERHEATING OF THE OXYGEN SENSORS.

1996 SERVICE CALIBRATIONS OLD P/N NEW P/N APPLICATION 16232427 16249467 S/T WITH L35+M50+NM8 16235818 16249468 S/T WITH L35+M50+NF2/NB6-Z49 16235819 16249469 S/T WITH L35+M50+NVF2/NB6+Z49 16235820 16249470 S/T WITH L35+M50+NN8 16235828 16249471 S WITH LF6+M50+NF2/NB6-Z49 16235829 16249472 S WITH LF6+M50+NF2/NB6+Z49 16235830 16249473 T WITH LF6+M50+NF2/NB6-Z49 16235831 16249474 T WITH LF6+M50+NF2/NB6+Z49

1997 SERVICE CALIBRATIONS OLD P/N NEW P/N APPLICATION 16256239 9360000 S/T WITH L35+M50+NB6/NF2- /NB6/NA3-Z49 16256240 9360001 S/T WITH L35+M50+NB6/NF2+Z49 16256241 9360002 S/T WITH L35+M50+NN8-NA7 16256242 9360003 S/T WITH L35+M50+NN8+NA7 16256243 9360004 S/T (2 DR) WITH L35+M50+NB6/NF2/NB6-Z49

16256244 9360005 S/T (2 DR) WITH L35+M50/NF2/NB6+Z49 16256247 9360006 S/T WITH LF6+M50+NB6/NF2-Z49 16256248 9360007 S/T WITH LF6+M50+NB6/NF2+Z49 16256250 9360008 S/T WITH L35+M50+NM8

IMPORTANT: THE CALIBRATIONS LISTED ARE FLASH CALIBRATIONS AND ARE NOT AVAILABLE FROM GMSPO. THESE CALIBRATIONS ARE AVAILABLE ON 1998 TECHLINE CD ROM DISC 07 AND LATER.

WARRANTY INFORMATION:

FOR VEHICLES REPAIRED UNDER WARRANTY, USE:

LABOR OPERATION DESCRIPTION LABOR TIME J6355 REPROGRAMMING 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.