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 MANUALSSUBARU1989XT 1.8 4, AUTOMATICREPAIR AND DIAGNOSISENGINE PERFORMANCESYSTEMSYSTEM/COMPONENT TESTSIDLE CONTROL SYSTEMBY-PASS AIR CONTROL VALVE (SPFI)
1989 Subaru XT 1.8 4, Automatic
By-Pass Air Control Valve (SPFI)
1989 Subaru XT 1.8 4, AutomaticSECTION By-Pass Air Control Valve (SPFI)
- With engine running, disconnect electrical connector. Engine speed should drop (a little with engine warm, a lot with engine cold). Reconnect electrical connector. Ensure engine speed returns to previous speed.
- If not, turn engine off. Turn ignition switch to "ON" position. Ensure 10-12 volts are available at Black/White wire of air control valve electrical connector.
- Turn ignition off. Ensure resistance of Air Control Valve (ACV) is 7.3-13 ohms. If not, replace ACV. Check ACV solenoid for any short to ground. If present, replace ACV.
- Attach electrical connector to ACV. Disconnect connector at ECU. Turn ignition on. Ensure 10-12 volts are present at Green/Red wire (terminal No. 45) of ECU. If not, check harness between ACV and ECU.
- Turn ignition off and reattach ECU connector. Turn ignition on. Backprobe Green/Red wire (terminal No. 45) of ECU. There should be 1 volt or less for about 1 minute after ignition is turned to "ON" position. After 1 minute, there should be at least 10 volts. If not, check for a bad ground, problem with ECU circuits (sensors) or ECU.
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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.