Auto Repair Help by Professional Mechanics
How
Does it Work /
How
an Idle Air Control Valve Works
How Does an Idle Air Control Valve Work? (IAC)
Introduction
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 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 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 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, also
inspect the IAC for a build-up on the seating (pointed) end and clean as
necessary.
Idle Air Control Valve (appearance will vary)
Common Problems
An IAC motor is highly susceptible to carbon and coking build up; if an 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 Toyota/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, also inspect the IAC for a
build-up on the seating (pointed) end and clean as necessary.
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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