Idle air control - know about them?

[highlandlake]

OK, I'm getting no response on the Chevy forum....and it's likely you guys know the answer just as well as the bowtie gang. On an idle air control valve (electrical component attached to a throttle body) is the pintle supposed to be seated in the hole while the engine is cold and not running? Or is the thing supposed to be telescoped into itself and away from the hole when cold and off? Trying to troubleshoot a hard starting condition. This IAC has a four prong electrical connector and I'm wary of testing it and don't know how to anyway. But I thought I'd start with whether or not their purpose is shutting off the intake hole when cold, or shutting off the hole when warm?
Mine (on the C-1500 truck) is positioned halfway but I can unscrew or screw it in to adjust. Just don't know whether it's OK as-is or not.
Thanks in advance, Tom

[Gizmo42]

I think its supposed to be in the middle when off then the ECU moves it in and out depending on the idle speed.

This is from the rodeo FSM..

Circuit Description
The powertrain control module (PCM) controls engine
idle speed with the idle air control (IAC) valve. To increase
idle speed, the PCM retracts the IAC valve pintle away
from its seat, allowing more air to bypass the throttle bore.
To decrease idle speed, it extends the IAC valve pintle
towards its seat, reducing bypass air flow. A Tech 2 will
read the PCM commands to the IAC valve in counts.
Higher counts indicate more air bypass (higher idle).
Lower counts indicate less air is allowed to bypass (lower
idle).

Idle Air Control (IAC) Valve
The Tech 2 displays the IAC pintle position in counts. A
count of “0” indicates the PCM is commanding the IAC
pintle to be driven all the way into a fully-seated position.
This is usually caused by a large vacuum leak.
The higher the number of counts, the more air is being
commanded to bypass the throttle blade.

Cleaning, Inspection, and Measurement
Procedure

Clean the IAC valve O-ring sealing surface, pintle
valve seat and air passage.
– Use carburetor cleaner and a parts cleaning brush
to remove carbon deposits. Do not use a cleaner
that contains methyl ethyl ketone. This is an
extremely strong solvent and not necessary for this
type of deposit.
– Shiny spots on the pintle are normal and do not
indicate misalignment or a bent pintle shaft.
– If the air passage has heavy deposits, remove the
throttle body for complete cleaning.

Inspect the IAC valve O-ring for cuts, cracks, or
distortion. Replace the O-ring if damaged.

In order to install a new IAC valve, measure the
distance between the tip of the pintle and the
mounting flange. If that measurement is 28 mm (1.1
in.) or less, the valve needs no adjustment. If the
measurement is greater than 28 mm (1.1 in.), apply
finger pressure and retract the valve. The force
required to retract the pintle on a new valve will not
damage the valve, shaft, or pintle.
NOTE: Do not push or pull on the IAC valve pintle on IAC
valves that have been in service. The force required to
move the pintle may damage it.
IMPORTANT: Use an identical replacement part in
order to replace a valve. IAC valve pintle shape and
diameter are designed for the specific application.

[rodeo02]

Yep, an IAC valve will open on a cold startup to bypass air around the throttle plate which increases idle speed. Only 3.2/3.5's up to 1999 have an IAC.

Joel

[highlandlake]

Dave & Joel,
Many thanks on the replies...I've learned something.
The bowtie boys have nothing on you!
Their forum gets more views and posts and I haven't heard a peep in three days about a component that is far more common on those engines.
I think I'm all set - I do have a pintle that is halfway to the seat when cold.
It just a got a good cleaning, and now I'll move on over to the EGR.
Also found that the plugs were gapped/worn .010" over spec. Can't wait to re-assemble this and hear it run.
My whole purpose in life right now is to tell my wife 'I told you so' when I get this truck to run good. When she saw me careen into the driveway with it (no plates or brakes) she told me to bring that ugly thing back from where you found it. Now what would you all do??