IAC (intake air control valve) (Page 1/1)
sledcaddie SEP 08, 08:19 PM
1985 SE with 2.8L 4 speed, 114,000 miles. I've got the plenum off to install stainless vacuum lines (yep, found a broken plastic one). While I'm in there, I thought I'd clean all the carbon out the IAC and throttle body port. If I just go ahead a install a new one, I've read on here that there is some procedure for "learning" for the new one? What does this involve? Before I buy a new one, is there a way to check the original to see if it is operating okay? Thanks, in advance, for any help.
Blacktree SEP 08, 10:05 PM
To reset the IAC, you jumper the diagnostic pins in the ALDL connector, then turn the key to the Run position (but don't start the engine). Wait about 10 seconds for the IAC to reset. Turn the key off, remove the jumper, and it's good to go.

You can also do that with your old IAC. After it resets, the valve should be fully closed. Then you can start the engine and let it idle. Unplug the IAC while it's idling, then shut off the engine. Check to see if the valve is partially open.

Side note: IAC stands for idle air control.
sledcaddie SEP 09, 01:11 PM
Some of the older posts state that the ECU will teach the new IAC during the first time it is driven. So, caIibrating isn't necessary. Is this accurate?
Gall757 SEP 09, 02:12 PM
go up to 40 mph for about 10 minutes and the learning should be complete.
theogre SEP 09, 02:26 PM
Above is not needed. Is part of directions how to set the Idle Stop screw on TB/TBI itself. See my Cave, Idle Stop
You only adjust the screw for replacement units or damage/maladjusted screws. Screw might move/wear over decades but Many morons think can adjust that screw but only make more problems that ECM and IAC may try to "fix" or not.

IAC will "reset" "relearn" itself ever time the car is driven over ~ 35mph in all Fiero and others w/ old GM OBD1 ECMs.

Note that you will often get high idle first after replacing or often cleaning IAC because you often mess w/ the motor to install/clean it.
The motor and valve must be "force" to retract when installed or can easy damage the IAC and TB/TBI seat the valve hits.

Most new ones have directions to retract out of the car. If not find same in most books and many web sites.
"Force" does not = much Force by you but directions to retract change a bit for different IAC types and should tell how to ID the type for directions at hand.
Take more effort then doing it wrong or IAC is binding for whatever etc.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

Blacktree SEP 09, 07:18 PM
Nobody said anything about adjusting the idle set screw. But yeah, you definitely shouldn't mess with it.

Also, if you use the reset procedure I described above, you won't have high idle. So you can just hop in the car and drive it. The idle re-learn will happen while you're driving.
sledcaddie SEP 09, 08:21 PM
Besides cleaning the carbon off, I reset the spindle length to the service manual specs of 28mm. It was about 30mm when I had removed it. Also found a broken vacuum line. So now, if the idle is corrected, I won't know which defect caused the "searching" idle.
Blacktree SEP 09, 09:43 PM
The 28mm spec is to make sure the IAC valve isn't damaged during installation. It will of course adjust its length as necessary.
fierogt28 SEP 09, 11:00 PM
The Ogre is right about the driving 35mph and over for the re-learn.

The correct size socket to remove the IAC is 32mm. Rodney has this tool for easier removal. I know, I have one.

And yes, the correct spec length to set the pintle on the IAC to base is 28mm or 1"1/8.

Be sure to follow Blacktree's set-up installation procedure.

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fierogt28

88 GT, Loaded, 5-speed.
88 GT, 5-speed. Beechwood interior, All original.