Legacy Outback Ltd Sedan F4-2.5L SOHC (2000)
Idle Speed: Description and Operation
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The ECM activates the idle air control solenoid valve in advance to control the amount of by-pass air flowing through the throttle valve in relation
to signals emitted from the crankshaft position sensor, engine coolant temperature sensor, pressure sensor and A/C switch. etc., so that the proper
idle speed specified for each engine load is achieved.
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The idle air control solenoid valve utilizes a duty solenoid design which the opening area of bypass port is changed by the amount of rotary valve
moving. For this reason, the by-pass air flow is regulated by controlling the duty ratio. The relationship between the duty ratio, rotary valve
moving and by-pass air flow is as follows:
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Duty ratio (high) -> Increases rotary valve moving and by-pass air flow.
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Bypass air control features the following advantages:
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Compensation for engine speed under A/C (air conditioning) system and electrical loads.
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Increase in idle speed during early stage of warm up period.
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A dashpot function during the time the throttle valve is quickly closed.
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Prevention of engine speed variations over time.