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is the IAC working?

B

BrApple

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I have a question about the Idle air controller works on the duratec and more specifically what is does it if fails.

when the controller goes bad will it cause a rough idle? I.E. would it cause the engine to vibrate more then normal?

I tried unplugging it on my svt and the idle dropped from the normal idle to about 250 rpm on the tach. When I plugged it back in you could hear it pulling air in when it openned back up. However the idle wasn't rough, just low.

On the car in question the idle didn't change at all when the controller was unplugged. When it was plugged back in there was no change in idle. The car however was idling at the correct 750 rpm according to the tach. It also idles very rough under 1k rpm. We tried adjusting the stop on the tb incase it just needed more air but then the idle would come back down to 750 rpm after a few seconds.

for reference the car has a hybrid running standard SE intake and heads, with a SVT PCM and injectors.
 
It's interesting you brought this up.

My car has had a low idle for a while now and I can't seem to find the cause of it. My IAC was original on the car, until earlier this year, when I swapped with another SVT UIM. When I swapped the UIM, I somehow forgot to plug in the IAC. The idle was no different than when it was plugged in, which is why I didn't notice.

When I found the IAC unplugged, I plugged it back in, reset the ECU and saw no change at all. Still idles the same as it did before, unplugged or plugged in.
 
well I do know the one in question is an older style/revision of the IAC, it has the horizontal connector, my SVT and SeVT have one with a connector at 90 degrees to the valve, so did the new one I put on My SeVT.


I will try unplugging the IAC on my SeVT the next time I run it and see what happens.

I was going to try my old IAC, which I believe is actually fine on the car and see what happens, but I'm thinking now that maybe it will not make a difference but I am not sure.
 
ok I did some data logging with my Xcal2 and learned the following.

Even if the IAC in unplugged the commanded idle is still the same.

With the IAC unplugged the idle dropped and the engine started to run alittle rough.

With the IAC unplugged the IAC Duty Cycle started to increase. When plugged in and working the duty cycle would come way down.



So would an engine with high compression and a none working IAC have a rought idle because it isn't getting enought air? The engine runs great at anything above 1k rpm.
 
I would call the Ford Performance help line at 1-800-FordSVT and ask for Jeff Dunne. He really knows a lot about that stuff.
 
FWIW When my IAC took a dump on my SVT it did so slowly. For a couple weeks (granted I don't drive the car all that often) when idling the rpm seemed a bit low. So I noticed it more and more going from the usual 750 down to about 700, then 650, then even below 600 there at the end and eventually it wouldn't idle at all. When driving it with the AC on i'd push in the clutch and the car would stall. Eventually it didn't even matter if I had the AC on or not it would kill every time I took my foot off the gas (even when starting it). Replaced the IAC and it has worked perfect since. The valve in mine must have been stuck or something and it wasn't allowing the proper amount of air into the manifold.

Either way I never really had a rough idle, just a low idle :shrug: So i'm not sure any of that really helps you.
 
I have had instances where the car will crank and not start. Cranking with my foot holding the accelerator cracked will usually allow the car to start. I attribute this to the IAC but it only happens about once a year (knock wood).
What is involved in IAC replacement? Should the procedure be posted in the how-to section?
 
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basically..... this is my understanding.

The IAC valve is a tiny little valve that works as an automated throttle body whenever the throttle is closed vaccume opens the IAC valve to allow air flow into the engine, JUST enough to keep it idleing, which is usualy around 750 rpms.
 
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