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 cars
computer or PCM (powertrain
control module) receives information from various sensors and will output signals
to adjust the idle air control motor in or out to adjust engine idle speed by controlling
engine idle air. An idle air control 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 idle air control motor to react slowly, either failure can cause the
engine to stall at idle. When a
trouble code scan is performed it sometimes won't always detect a failed or
weak idle air control motor.
To check the idle air control motor remove the unit, with the wires connected
turn the key to the "on" position without starting the
engine, the idle air control should
move in or out. If the idle air control motor does nothing it has probably failed,
replace it with a new unit and recheck system. Note: while the idle air control
motor is removed clean (use aerosol carburetor cleaner) the passages the idle air
control uses to control idle air speed, also inspect the idle air control for a
build-up on the seating (pointed) end and
clean as necessary.
Idle Air Control Valve (appearance will vary)
Common Problems
An idle air control motor is highly susceptible to carbon and coking build up;
if an idle air control 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 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 idle air control like
Toyota and Lexus is subject to carbon and should be cleaned about every 40,000 miles
to avoid stalling.
Basic Maintenance
To check the idle air control motor remove the unit, with the wires connected
turn the ignition key to the
"on" position without starting the engine, the idle air control should move in or
out. If the idle air control motor does nothing it has probably failed, replace
it with a new unit and recheck system. Note: while the idle air control motor is
removed clean (use aerosol carburetor cleaner) the passages the idle air control
uses to control idle air speed, also inspect the idle air control for a build-up
on the seating (pointed) end and clean as necessary.
If further assistance is needed, our certified car repair technicians are ready
to answer your car questions.
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