Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCADILLAC1991FLEETWOOD FWD V8-300 4.9LREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSRELAYS AND MODULES - COMPUTERS AND CONTROL SYSTEMSIDLE/THROTTLE SPEED CONTROL UNITDESCRIPTION AND OPERATIONIDLE SPEED CONTROL (ISC) MOTOR
1991 Cadillac Fleetwood FWD V8-300 4.9L
Idle Speed Control (ISC) Motor
1991 Cadillac Fleetwood FWD V8-300 4.9LSECTION Idle Speed Control (ISC) Motor
Throttle Body Assembly - Exploded View:
The Idle Speed Control (ISC) Motor is mounted on the throttle body and is used to control engine idle speed. The ISC plunger acts as a moveable throttle stop changing the primary throttle valve angle. The ECM/PCM monitors engine idle speed and moves the ISC plunger (throttle stop) to maintain the desired idle speed required for the operating condition.
An integral part of the ISC is the throttle switch. The position of the throttle switch determines whether or not the ISC controls idle. When the throttle lever rests against the ISC plunger, the switch contacts are closed and the ECM/PCM moves the ISC plunger to the programmed idle speed position. When the throttle lever breaks contact with the ISC plunger, the switch contacts open and the ECM/PCM stops sending idle speed commands. Engine speed is again controlled by the accelerator pedal.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.