IDLE SPEED VARIES A/C CLUTCH NEW PROM INFORMATION

A REVISED PROM CALIBRATION HAS BEEN RELEASED FOR 1983 HT4100-EQUIPPED VEHICLES TO PROVIDE A MORE RESPONSIVE IDLE SPEED CONTROL ACTION, WHICH REDUCES IDLE SPEED VARIATIONS CAUSED BY COMPRESSOR CLUTCH ENGAGEMENT. THIS CONDITION MAY BE DESCRIBED AS (1) AN IDLE SHAKE OR VIBRATION, WHICH OCCURS AS IDLE SPEED DROPS DUE TO COMPRESSOR CLUTCH ENGAGEMENT, OR (2) AN INCREASE (SURGE) IN IDLE SPEED WITHIN THE RANGE CONTROLLED BY THE ISC AS THE ISC COMPENSATES FOR THE A/C COMPRESSOR LOAD. DIAGNOSE AN UNSTEADY IDLE SPEED CONDITION ON 1983 HT4100-EQUIPPED VEHICLES, WHICH OCCURS ONLY WITH THE AIR CONDITIONING ON, AS FOLLOWS: 1.ENTER DIAGNOSTICS AND PERFORM SWITCH TESTS. THE CAR MUST PASS THE DRIVE AND REVERSE SWITCH TESTS (.7.3 AND .7.4). SHIFT SLOWLY AND DELIBERATELY FROM NEUTRAL TO DRIVE TO NEUTRAL, LOOKING FOR THE CHANGE. A DRIVE SWITCH WHICH IS MISADJUSTED, OR DOES NOT ENGAGE UNTIL SHIFTED INTO MANUAL THIRD, MAY NOT BE DETECTED IF THE LEVER IS FORCED QUICKLY PAST DRIVE INTO 3, 2, OR 1. 2.VERIFY THAT THE VEHICLE PASSES SWITCH TEST .8.0 (ECC COMPRESSOR CLUTCH INPUT). 3.CHECK THROTTLE SWITCH FOR INTERMITTENT OPERATION USING THE STATUS INDICATOR LIGHT ON THE ECC PANEL. (WITH AVAILABLE FORCE, THE SWITCH MAY BE ON THE EDGE OF TRIPPING.) 4.CHECK PARAMETER .1.3 TO DETERMINE THE GENERATION OF PROM PRESENT. IF AN EARLIER GENERATION PROM (LOWER NUMBER PARAMETER .1.3 PROM ID) IS PRESENT, REPLACE IT WITH THE NEW GENERATION PROM AS SHOWN BELOW: PROM INK STAMP ON PROM SERVICE PROM P/N PROM ID PARAM .1.3 C FEDERAL CTK 1226529 14 C CALIFORNIA CTL 1226530 24 C EXPORT CTM 1226531 33 C ALTITUDE CTW 1226538 123 C SWISS/SWEDEN CTZ 1226541 34 E/K FEDERAL CTN 1226532 44 E/K FEDERAL DIGITAL CTS 1226535 74 E/K CALIFORNIA CTP 1226533 54 E/K CALIFORNIA DIGITAL CTT 1226536 84 E/K ALTITUDE CTX 1226539 153 E/K ALTITUDE DIGITAL CTY 1226540 183 E/K EXPORT CTR 1226534 63 E/K EXPORT DIGITAL CTU 1226537 93 E/K SWISS/SWEDEN CUA 1226542 64 E/K SWISS/SWEDEN DIGITAL CUB 1226543 94

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.