IAC behavior

Some time ago, I started a thread on problem starting at or near 32.
And backyard mechanics told me it was probably my IAC,
Well I removed it, it's not grounded, the resistance between the posts is
10ohms, sounds OK, the voltage that goes to it is 12.5V.
But should the IAC normally closed or open when I turn the switch to ON.
When the switch is OFF, should the valve be closed or open?
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Correct me if I am wrong , but the way I understand the IAC is :
Closed when OFF
Partially (variably) open when engine running ( it receives pulses from the ECM)

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Yves opined in

If the thing idles ok, in warmer weather and once started, there's no reason to test it. just spray it out good with intake cleaner, and also the throttle area.
Closed with key off, I believe..I'd tell you for sure but the book isnt handy.
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Well, the van still doesn't start well, but it idles relatively ok, I have a small miss at random.
The IAC unplugged looks as if it's half way open.
When pluged, ignition key on , it's still half way open.
I thought that applying 12V, should close or open the valve!

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That is because the IAC valve gets it's instructions (in terms of voltage) from the ECM, not from a hot ignition. You should see the valve open partly or full in fast-idle mode when you first turn the engine on, until kick-down. The fast-idle warms up the cold engine by allowing more air into the intake, increasing the idle speed to shorten the time it takes to get the engine up to operating temperature. That is the basic concept, anyway. Some of the Chilton manuals have great descriptions on how the ECM controls the different states of the intake components: idle, fast-idle, wide-open throttle (WOT) and limp mode.
Simply turning the ignition on won't actuate the valve, the engine must be running. A catch-22 if you are trying to determine how much the valve is opening, because the engine won't run without the valve installed. One question, what do you mean by "doesn't start, but idles OK"?
Matt
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I did not say "doesn't start, but idles OK",
I said "Well, the van still doesn't start well, but it idles relatively ok"
I should have said the van is hard to start!!!
Sometime to start it I need to put the throttle to the floor, as if the engine is not getting enough air or too much gas, any ways, the mixture gas/air doesn't seem ok.
Thank.s

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Yves opined in

Again, the ECM has an algorythm that mimics a carburetor while starting.
Holding the pedal to the floor opens the choke on a carb and has the ecm send LESS gas on EFI
Pumping (or touching) the pedal squirts gas in a carb, and sends MORE gas on an EFI
On my Taurus, when it was starting hard in cold weather , i found that I could pump the pedal twice THEN hold it to floor to get it to start quicker, but then it ran rough for a minute or two because I had set the wrong table in the ECM.
Cleaning the Throttle body and IAC, IN MY CASE, fixed the problem.
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Hi,
What did you use to clean the IAC.

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Hi again,
If I change the IAC, will I need to go to Ford to have it ajusted?

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wrote:

There is no adjustment of the IAC. You need to reset the ECM either by using a scan tool or by disconnectiong the battery for at least 10 minutes. When you restart the engine, don't touch the throttle. This allows the ECM to start the engine using a basic set of parameters programed at the factory. Once the engine is started, stand back and let it idle for at least 2 minutes to allow the ECM to go thru it's startup timing to closed loop operation. While holding the brake, place the trans selector in each of it's positions several times for a few seconds each without touching the throttle. This allows it to learn the idle speed droop for the transmission. You should then drive it around a few miles for it to complete relearning of the engine operating parameters. If you still have the problem, you will need to do a bit more diagnostic work. In the end, you may find it would have been cheaper and less hassle to have a competent tech run a diagnostic on it for about $75US. It can get very expensive throwing parts at it until you get the right one.
Good luck
Lugnut

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There is an ajustment knob on the IAC, and it's said in the Haynes manual not to touch it unless you are a Ford Tech.
And Ford tech can't find anything... well after the 75US!!!

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Than the IAC has no adjuster and is totally controlled by the computer. The only manual adjustment is probably the throttle stop screw, which is near the IAC.
Matt
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opined in

yeah... I was wondering.
DO NOT adjust that stop screw!
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Well,
What if I turned it a bit?

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It's not the throttle stop screw, it's a black button on the side of the IAC.
On the IAC it is said "Do not turn the button CCW"

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You should'nt touch anything, unless you're ready for a headache...
If the engine is hard to start, but runs relatively well once started, try to start it while pressing a little bit on the gas (just barely), if it starts fine, remove the IAC and clean it with throttle body cleaner... if it doesn't help...well replace the IAC
Good luck

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So much for the little black button. What is it? What is it for? Why should it not be turned?
Yves wrote:

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1) Because it won't fix your problem.
2) If you do and your car no longer idles correctly or throws error codes you will need a tachometer or dvm to try to back to the factory setting.
The throttle stop setting affects the output signal of the throttle position sensor, so there is no need to send the computer the wrong signal from the TPS for the computer can send everything else the wrong information about the current throttle state.
Matt
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Martin F. O'Rourke opined in

For the same reason as you shouldnt mess with the throttle stop screw.
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