TPS MINIMUM AIR AND ISC ADJUSTMENT GUIDELINES

THE FOLLOWING PROCEDURE SHOULDBE USED IN CONJUNCTION WITH ADVANCE INFORMATION SHOP MANUAL ST-356-81 WHEN REPLACING OR SERVICING AN IDLE SPEED CONTROL ASSEMBLY. IDLE SPEED CONTROL (ISC) THE IDLE SPEED CONTROL (ISC) IS CONTROLLED BY THE ELECTRONIC CONTROL MODULE (ECM) WHICH HAS THE DESIRED IDLE SPEED PROGRAMMED IN ITS MEMORY. THE ECM COMPARES THE ACTUAL IDLE SPEED FROM THE ENGINE RPM SENSOR (DISTRIBUTOR TACH OR EST REFERENCE SIGNAL) TO THE DESIRED RPM REFERENCE IN MEMORY. WHEN THE TWO DO NOT MATCH, THE ISC PLUNGER IS MOVED IN OR OUT. THIS AUTOMATICALLY ADJUSTS THE THROTTLE TO HOLD AN IDLE RPM INDEPENDENT OF THE ENGINE LOADS. AN INTEGRAL PART OF THE ISC IS THE THROTTLE CONTACT SWITCH. POSITION OF THE SWITCH DETERMINES WHETHER OR NOT THE ISC SHOULD CONTROL IDLE SPEED. WHEN THE THROTTLE LEVER IS RESTING AGAINST THE ISC PLUNGER, THE SWITCH CONTACTS ARE CLOSED AT WHICH TIME THE ECM MOVES THE ISC TO THE PROGRAMMED IDLE SPEED. WHEN THE THROTTLE LEVER IS NOT CONTACTING THE ISC PLUNGER, THE SWITCH CONTACTS ARE OPEN AND THE ECM STOPS SENDING IDLE SPEED COMMANDS AND THE DRIVER CONTROLS ENGINE SPEED. REPLACEMENT 1.WITH IGNITION "OFF", DISCONNECT WIRING FROM ISC MOTOR AND REMOVE SCREWS (2) THAT ATTACH THE ISC BRACKET TO THE CARBURETOR AND REMOVE ISC AND BRACKET ASSEMBLY. 2.INSTALL NEW IDLE SPEED CONTROL (ISC) ASSEMBLY TO CARBURETOR AND RE-ATTACH THROTTLE RETURN SPRING AND ANY OTHER RELATED PARTS REMOVED DURING DISASSEMBLY. PERFORM THE "ON-CAR" SPEED ADJUSTMENTS NOTED BELOW. "ON-CAR" SPEED ADJUSTMENTS DO NOT USE THE ISC PLUNGER TO ADJUST CURB IDLE SPEED AS THE IDLE SPEED IS CONTROLLED BY THE ECM. WHEN A NEW IDLE SPEED CONTROL (ISC) ASSEMBLY IS INSTALLED, A BASE (MINIMUM AUTHORITY) AND HIGH (MAXIMUM AUTHORITY) RPM SPEED CHECK MUST BE MADE AND ADJUSTMENTS MADE AS REQUIRED. THESE ADJUSTMENTS LIMIT THE LOW AND HIGH RPM SPEEDS TO THE ECM. WHEN MAKING A LOW AND HIGH SPEED ADJUSTMENT, THE LOW SPEED ADJUSTMENT IS ALWAYS MADE FIRST. ** SEE BULLETIN FOR ADDITIONAL TEXT & ILLUSTRATIONS **

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