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THE IDLE CONTROL VALVE - PART 2
Submitted by Bluegrass / 06-02-06
- The IAC is an air bypass controller powered by the computer
in response to engine idle RPM requirements and some other control
actions.
- The idle air intake can be thought of as two parallel airflow
paths consisting of the slightly open throttle blade and the IAC
bypass opening.
- The throttle opening is set just enough open to allow the engine
to 'low' idle about 550 rpm +/- in the absence of IAC opening
control.
- The IAC is pulse controlled by the computer in response to inputs
from the distributor, coolant temp sensor, intake air temp, idle
loads from A/C/ heating, lights etc. It plays a large part in
overall drivability from cold starting high-idle to small load
idle compensations to deceleration fuel control.
- Problems: If this device sticks or become faulty in any way,
idle control is affected for all above events.
- Testing: At hot idle, remove the connector. Does the engine
idle drop? If yes it is working. If no, there is a fault with
its operation.
- Cleaning: Remove and spray clean with special throttle body
cleaner until all the carbon liquid and gum has been flushed out
of the 'pintel' area and the pintel is free to move though it's
total range against it's spring loading.
Additionally now is a good time to clean the throttle body thru
the large air intake hose opening by holding the throttle blade
open and cleaning all it's internal diameter until the cleaner flows
back out clean onto paper or a rag. The motor may show difficulty
in starting right away with cleaner inside the intake until it evaporates.
- Testing operation to precise limits: Hook an older ignition
Dwell meter across the IAC and watch the needle as the IAC is
being signaled. Look at the changes as loads are applied like
A/C or lights. This should tell how well the control system works
if the idle stays solid.
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