The idle air control valve is responsible for controlling the engine idle
speed via the car's PCM (computer). These valves are configured differently
depending on manufacturer but perform the same task. The IAC or ISC valve as it's called diverts
engine intake air from the main
throttle body and bypasses a
portion of the intake air to control idle speed. When the idle speed cannot be
controlled it will trigger a check engine light (MIL) due to idle speed
fluctuations. On newer cars (2000 - 2005) depending on manufacturer this valve
is being phased out as electronic throttle systems are becoming commonplace.
What goes wrong?
As a car ages the IAC will become dirty (a condition called coking) due to
the volumes of air processed through the valve. Heavy particles in the air
attach themselves to the valve's internal parts making it difficult for the
valve to operate.
Idle Air Control
Controls engine idle speed
Needs service when the engine is tuned up
Is located near the intake throttle body
Can fail making a honking noise (Ford)
Easy to replace/service in most cases
Can cause a check engine light
Will cause engine idle fluctuations
May cause the engine to stall at idle
Can cause the engine to idle too high.
Where is it?
The idle air control valve (IAC) is located near the throttle body of the
intake manifold in most cases. Additional designs include rubber hoses running
from the throttle body and air intake tube to a remote valve.
What's the cost?
The cost of an IAC will vary but typically will run between $60.00 and $120.00
US. If you are not changing the valve yourself labor costs will be minimal
because of the easy access to the valve. If the valve is mounted to the bottom
of the throttle bore such as in Toyota products the cost will run slightly more. To
service the IAC separately the cost should be applicable to the vales location.
Most services of this kind are included in a major tune up.
Locate the IAC valve on your engine. If your car does NOT have a
throttle cable you do not have an IAC valve, this is the best way to tell
what kind of system your car has. For this example we have removed the
throttle bore and cleaned
once completed remove the mounting screws to the idle air control valve. You
might need to use a impact screwdriver to get the screws undone.
This image shows the coking condition similar to the throttle
actuator/bore which causes erratic operation of
the valve, stalling and high idle can
be the result.
Use carburetor cleaner to spray the valves internal parts using a
shop towel to help wipe away deposits (clean the valve thoroughly). This
can take some time so you may need to let the valve soak in cleaner
depending on the level of coking while
idle air valves need to be replaced due to internal wear.
The IAC gathers air from internal ports inside the intake and throttle
bore systems. These transfer ports need to be serviced as well when cleaning
the IAC motor to help keep the newly cleaned valve working correctly.
Make sure all gaskets or seals are in good shape
to avoid leakage as you reinstall the valve onto the throttle bore housing and
reinsert the mounting screws to tighten evenly.