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 MANUALSSUBARU2002LEGACY GT WAGON AWD F4-2.5L SOHCREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSDESCRIPTION AND OPERATIONIDLE AIR CONTROL
2002 Subaru Legacy GT Wagon AWD F4-2.5L SOHC
Idle Air Control
2002 Subaru Legacy GT Wagon AWD F4-2.5L SOHCSECTION Idle Air Control
- The ECM activates the idle air control solenoid valve to control the bypass air flowing through the bypass passage in the throttle body depending on signals from the crankshaft position sensor, engine coolant temperature sensor, pressure sensor and A/C switch so that the proper idle speed for each engine load is achieved.
- The idle air control solenoid valve uses a duty-ratio-controlled solenoid which can continuously vary the opening area of the rotary valve. As the ECM increases the duty ratio, opening of the rotary valve increases so that the bypass air flow increases, and the engine idling speed becomes higher as a result.
- The bypass air control is necessary for:
- Increasing idling speed when the air conditioning system and/or electrical loads are turned on.
- Increasing idling speed during early stage of warm up period.
- Obtaining dashpot function when the throttle valve is quickly closed.
- Prevention of engine speed variation during idling.
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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.