Mechanics

Idle Air Control Valve

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
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.

Related Car Repair Information

AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


COMMENTS TO THIS ARTICLE


Please use our question form if you have a specific question about your car as we are not able to give you a full answer on this page.



Article first published (Updated 2013-11-21)