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 MANUALSJEEP1987WRANGLER S, 4.2 C, AUTOMATICREPAIR AND DIAGNOSISENGINE PERFORMANCESYSTEM2.5L TBI SYSTEMCOMPONENT TESTINGCLOSED THROTTLE SWITCH
1987 Jeep Wrangler S, 4.2 C, Automatic
Closed Throttle Switch
1987 Jeep Wrangler S, 4.2 C, AutomaticSECTION Closed Throttle Switch
NOTE:
It is important that all testing be done with the idle speed actuator (ISA) motor plunger in the fully extended position (as it would be after a normal engine shut down). If it is necessary to extend the motor plunger to test the switch, an ISA motor failure can be suspected. Refer to ISA motor test.
- With ignition on, connect voltmeter positive lead to pin 13 of diagnostic connector D2. Attach negative lead to pin 7. Voltage should be close to zero at closed throttle and greater than 2 volts at any position other than closed throttle.
- If the voltage is always zero, test for a short circuit to ground in the wiring harness or switch. Test for an open circuit between pin 25 of ECU connector and throttle switch.
- If voltage is always more than 2 volts, test for an open circuit in the wiring harness between the ECU and switch connector. Also check for open circuit between the switch connector and ground. Repair or replace wiring harness as needed.
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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.