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.
1990 Mercury Grand Marquis LSFACTORY OEM SERVICE PROCEDURE
ISC Motor (CFI)
- Turn key off and wait 10 seconds. Disconnect harness from DC motor. Using jumper wires, connect ISC positive (+) circuit of DC motor to battery positive (+) terminal. Connect ISC negative (-) circuit of DC motor to battery negative terminal for 4 seconds.
- Motor shaft should extend more than 2" (51 mm). Connect ISC (+) circuit of DC motor to battery negative terminal and ISC (-) circuit of DC motor to battery positive terminal for 4 seconds. Motor shaft should retract to less than 1 3/4" (44 mm). If motor shaft does not move in and out as indicated, replace DC motor.
Factory Service Tools
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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.
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