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 Geo Tracker L4-1590cc 1.6LFACTORY OEM SERVICE PROCEDURE
Idle/Throttle Speed Control Unit: Service and Repair
ON VEHICLE SERVICE:
1. With the ignition switch OFF, disconnect the ISC solenoid valve coupler.
2. Connect an ohmmeter to each ISC solenoid valve terminal and measure resistance. Resistance should be 5.4-6.6 ohms at 20°C (68°F). If resistance is out of specification, replace the ISC valve.
REMOVAL:
1. Disconnect the negative battery terminal.
2. Disconnect the ISC solenoid valve coupler.
3. Remove the ISC solenoid valve wire harness terminals from the coupler after unlocking the terminal lock of coupler.
4. Remove the ISC solenoid valve from the throttle body.
CAUTION: The ISC solenoid valve is an electrical component and must NOT be soaked in any liquid solvent or cleaner. Otherwise damage may occur.
5. Connect battery voltage to the ISC solenoid valve terminals momentarily (within 1 second) and disconnect it immediately. While doing so, check the valve for operation. When another check is necessary, wait for longer than 10 seconds before rechecking. Refer to DIAGNOSIS AND TESTING PROCEDURES/DIAGNOSTIC CHARTS/C CHARTS/CHART C2.
INSTALLATION:
1. Install the ISC solenoid valve into the throttle body.
2. Install the ISC solenoid valve wire terminals into the coupler and install the terminal lock.
3. Reconnect the ISC solenoid valve coupler.
4. Reconnect the negative battery terminal.
ISC Solenoid Valve Resistance Check:
1. With the ignition switch OFF, disconnect the ISC solenoid valve coupler.
2. Connect an ohmmeter to each ISC solenoid valve terminal and measure resistance. Resistance should be 5.4-6.6 ohms at 20°C (68°F). If resistance is out of specification, replace the ISC valve.
REMOVAL:
1. Disconnect the negative battery terminal.
2. Disconnect the ISC solenoid valve coupler.
3. Remove the ISC solenoid valve wire harness terminals from the coupler after unlocking the terminal lock of coupler.
4. Remove the ISC solenoid valve from the throttle body.
CAUTION: The ISC solenoid valve is an electrical component and must NOT be soaked in any liquid solvent or cleaner. Otherwise damage may occur.
ISC Solenoid Valve Operation:
5. Connect battery voltage to the ISC solenoid valve terminals momentarily (within 1 second) and disconnect it immediately. While doing so, check the valve for operation. When another check is necessary, wait for longer than 10 seconds before rechecking. Refer to DIAGNOSIS AND TESTING PROCEDURES/DIAGNOSTIC CHARTS/C CHARTS/CHART C2.
INSTALLATION:
1. Install the ISC solenoid valve into the throttle body.
2. Install the ISC solenoid valve wire terminals into the coupler and install the terminal lock.
3. Reconnect the ISC solenoid valve coupler.
4. Reconnect the negative battery terminal.
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.