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How
Does it Work /
How
an Idle Air Control Valve Works
How Does an Idle Air Control Valve Work? (IAC)
An IAC (idle air control) motor is designed to adjust the engine idle RPM speed
by opening and closing an air bypass passage inside the throttle body. The car computer
or ECM (electronic control module) receives information from various sensors and
will output signals to adjust the IAC motor in or out to adjust engine idle speed
by controlling engine idle air. An IAC motor can fail one of two ways, either the
motor short circuits and stops working or the motor will develop high resistance
and cause the IAC control motor to react slowly, either failure will cause the engine
to stall at idle. When a trouble code scan is performed it sometimes won't always
detect a failed or weak IAC motor. To check the IAC motor remove the unit, with
the wires connected turn the key to the "on" position without starting the engine,
the IAC should move in or out. If the IAC motor does nothing it has probably failed,
replace it with a new unit and recheck system. note: while the IAC motor is removed
clean (use aerosol carburetor cleaner) the passages the IAC uses to control idle
air speed.
Idle Air Control Valve
Common Problems
An IAC motor is highly susceptible to carbon and coking build up, if a IAC
goes too long without cleaning it can cause stalling and poor idle quality. Some
cars are designed with a large vacuum transfer hose that connects the intake
manifold to the IAC (idle air control) motor. If a broken or dilapidated these
vacuum lines can cause the engine to lose vacuum which will allow the
engine to run rough
and die. Inspect all engine and accessory vacuum lines to look for missing, torn
or dilapidated lines and replace as needed. Any car that is designed with a
magnetic non-motor operated IAC like Lexus is subject to carbon and should be
cleaned about every 40,000 miles to avoid stalling.
Basic Maintenance
To check the IAC motor remove the unit, with the wires connected turn the key
to the "on" position without starting the engine, the IAC should move in or out.
If the IAC motor does nothing it has probably failed, replace it with a new unit
and recheck system. note: while the IAC motor is removed clean (use aerosol
carburetor cleaner) the passages the IAC uses to control idle air speed
How
Does it Work /
How
an Idle Air Control Valve Works
Check Manufacturer Specific IAC Idle
Air Control Questions and Answers
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