OK MOST LIKLEY WE HAVE A VACUM LEAK ISSUE HERE SO CHECK VACUM SYSTEM FOR ANY LEAKS FIRST
READ BELOW HOW SYSTEM WORKS , IF VACUM GOO CHECK SERVO THEN GO TO SWITCH
1988 Ford Truck F 250 2WD Pickup V8-7.3L DSL
DESCRIPTION The speed control system is composed of On-Off, Set-Acc, Coast and Resume (if equipped) switches. The system contains vacuum hoses, servo (throttle actuator) assembly, speed sensor, amplifier, check valve assembly, and depending on model and year, a clutch switch, stop light switch or vacuum dump valve. Models with resume, also use a vacuum reserve tank.
OPERATION To operate speed control system, engine must be running and vehicle speed must exceed 30 mph. When On-Off switch is actuated, the system is ready to accept a set speed signal. With On switch engaged, vehicle speed exceeding 30 mph and stable, depress the Set-Acc button. The speed now set will be maintained until brake pedal is depressed, system is turned off or a new speed has been set.
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