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 MANUALSMERCURY1991COUGAR LS, 3.8 4REPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROLS - SYSTEM/COMPONENT TESTS - 3.8LIDLE CONTROL SYSTEM
1991 Mercury Cougar LS, 3.8 4
Idle Control System
1991 Mercury Cougar LS, 3.8 4SECTION Idle Control System
NOTE:
See Idle Air Control Valve (IAC) and Idle Speed Control Solenoid (ISC) test procedures under SOLENOIDS. Curb idle and fast idle speed is controlled by the ECA, and is not adjustable. Some throttle bodies have a sludge-tolerant design with a special coated throttle bore. A Yellow/Black warning decal on these units warns against backing off throttle plate adjustment screw to avoid throttle plate sticking in bore. Faults in idle control system components or circuit should set a service code. See Quick Test procedure in the appropriate TESTS W/CODES
article.
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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.