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Home >> Subaru >> 1991 >> XT Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System/Component Tests >> Idle Control System >> By-Pass Air Control Valve (TBI)
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By-Pass Air Control Valve (TBI)

  1. 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.
  2. 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.
  3. Turn ignition off. Ensure resistance of Air Control Valve (ACV) is 7.3-13 ohms at -4 to 176°F (-20 to 80°C). If not, replace ACV. Check ACV solenoid for any short to ground. If present, replace ACV.
  4. Attach electrical connector to ACV. Disconnect connector at ECU. Turn ignition on. Ensure 10-12 volts are present at terminal No. 45 (Green/Red wire) of ECU. If not, check harness between ACV and ECU.
  5. Turn ignition off and reconnect ECU connector. Turn ignition on. Backprobe terminal No. 45 (Green/Red wire) of ECU. There should be one volt or less for about one minute after ignition switch is turned to ON position. After one 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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