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Old 06-03-2011, 05:38 PM   #1
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Idle Question

First of all, sorry this is just a random post in a forum but I'm on my phone and didn't see a mechanic/problem thread.

I've got a 2003 v6 and when I start my car it idles up to around 2500, slowly drops and will randomly rev up while I'm driving. We googled the problem and on multiple mustang forums people having the same problem were told to replace the IAC.

We replaced the IAC and are still having the same problem. Checked it and its holding it open. Got 13.3 volts to it at idle.

Unpluging the tps didn't do anything and as far as we know I don't have any vacuum leaks.

I wanna know what controls the reading to the IAC; what tells it to open and close? Or any suggestions as to what may be going on.

Thanks and again, sorry for this being in a random forum!
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Old 06-03-2011, 06:10 PM   #2
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If that was the case we would all have to say sorry for random threads... Lol. Need more information like when it idles is it rough? Give little more details... Ima do some research and see
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Old 06-03-2011, 06:11 PM   #3
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Do u have a cai?
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Old 06-03-2011, 06:27 PM   #4
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I did have a cai, but went back to the factory air box bc we noticed it started when we switched to the after market one.

It's not a rough idle, pretty clean actually.

My check engine light is on and I know it throws an o2 censor code which we bought and are putting in when it arrives. We're headed to the dealership my fiance works at to use their diagnostic scan tool to see if there is any other codes.
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Old 06-03-2011, 06:37 PM   #5
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Hmmm...
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Old 06-03-2011, 06:38 PM   #6
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Well I changed my iac too bc of this same issue... Do you have a tuner?
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Old 06-03-2011, 06:39 PM   #7
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And I assume you keep up your tune ups?
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Old 06-03-2011, 06:39 PM   #8
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Throwing codes for
p1504 - iac control circuit
P0705 - transmission range (prndl input)
P1507 - iac underspeed error (see p0506)

My fiance is checking alldata now.
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Old 06-03-2011, 06:41 PM   #9
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No tuner. And yes, I keep up with the tune ups.
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Old 06-03-2011, 06:42 PM   #10
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No tunes and yes, tune ups are kept up with.
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Old 06-05-2011, 12:13 PM   #11
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We still have no idea what's going on. It's really pissing me off. Lol.

I think we're doing the o2 sensor today. Idk if it'll help anything but it needs it done anyways.
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Old 06-05-2011, 01:02 PM   #12
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Quote:
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We still have no idea what's going on. It's really pissing me off. Lol.

I think we're doing the o2 sensor today. Idk if it'll help anything but it needs it done anyways.
This might be outa the box but are your converters clean?
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Old 06-05-2011, 01:54 PM   #13
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Have you cleaned the MAF sensor yet?
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Old 06-06-2011, 07:08 AM   #14
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I'm not 100% sure how to check the converters. And we cleaned the maf sensor with maf sensor cleaner.
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Old 06-06-2011, 08:54 AM   #15
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Re: Idle Question

I just changed my iac because my car would idle high at like 3000. If you just recently swapped the iac - unplug your battery n leave it unplugged for about 10 mins (usually 5, just to be sure i do 10 and i time it), plug it back in and turn ur car on and let it run for about 5 mins. That should fix the problem, let me know!
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Old 06-06-2011, 09:02 AM   #16
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Quote:
Originally Posted by CHILE10_STANG
I just changed my iac because my car would idle high at like 3000. If you just recently swapped the iac - unplug your battery n leave it unplugged for about 10 mins (usually 5, just to be sure i do 10 and i time it), plug it back in and turn ur car on and let it run for about 5 mins. That should fix the problem, let me know!
Okay, I was thinking it might have to relearn it, but wasn't sure. I'll do that tonight and see if it helps. Thank you!
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Old 06-06-2011, 10:00 AM   #17
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Re: Idle Question

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Okay, I was thinking it might have to relearn it, but wasn't sure. I'll do that tonight and see if it helps. Thank you!
no problem bro... like u said, it has to relearn it. make sure u time it so u dont do it for too little
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Old 06-06-2011, 10:11 AM   #18
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Originally Posted by CHILE10_STANG

no problem bro... like u said, it has to relearn it. make sure u time it so u dont do it for too little
We relearned it when we put the factory air box back on, but not when we did the iac. Hopefully it'll work.
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Old 06-06-2011, 10:26 AM   #19
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Re: Idle Question

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Originally Posted by vintagel0verr View Post
We relearned it when we put the factory air box back on, but not when we did the iac. Hopefully it'll work.
it will for sure, same thing happened with mine!
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Old 06-07-2011, 10:35 AM   #20
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You have a vacuum leak. Throw smoke in a port common to both banks and look for the leak.
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Old 06-07-2011, 10:56 AM   #21
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Re: Idle Question

a gunked up maf can cause the car to idle very odd, my 01 would hang at a high rpm in neutral and many v6's do this. A tune can modify the idle decay rate~ I think thats also part of it.
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Old 06-07-2011, 11:43 AM   #22
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Dirty throttle body?
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Old 06-07-2011, 08:50 PM   #23
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Relearning the iac right now. If that doesn't work, I'll check the other.

Thanks y'all with the help. I really was at a loss for words. Lol.
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Old 06-07-2011, 09:13 PM   #24
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Well, relearning the iac didn't help the problem.

Back at square one. Lol.

Maf sensor is cleaned, throttle body is cleaned.

What communicates the iac to open and close? It's holding it wide open. That's why we replaced it, bc we thought it was a problem with the solenoid. Would cleaning the maf sensor cause problems?
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Old 06-07-2011, 09:18 PM   #25
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Quote:
Originally Posted by vintagel0verr
Well, relearning the iac didn't help the problem.

Back at square one. Lol.

Maf sensor is cleaned, throttle body is cleaned.

What communicates the iac to open and close? It's holding it wide open. That's why we replaced it, bc we thought it was a problem with the solenoid. Would cleaning the maf sensor cause problems?
Honestly mine is doing the same thing. I'm interested in what y'all come up with. I just closed my throttle body so I could get the idle down. But I would like to fix it correctly. I'll research it some and see if I can't find something
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Old 06-07-2011, 09:26 PM   #26
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YOU HAVE A VACUUM LEAK. You find that, your problem is fixed. Put a vacuum gauge on it and see if the gauge is fluttering.
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Old 06-07-2011, 09:32 PM   #27
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Originally Posted by 254S197
YOU HAVE A VACUUM LEAK. You find that, your problem is fixed. Put a vacuum gauge on it and see if the gauge is fluttering.
See that was what I was looking for. But why would the iac hang open? Wouldnt it close to try and compensate for the leak?
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Old 06-07-2011, 09:36 PM   #28
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A vacuum leak will cause idle surge. The iac is fine.
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Old 06-07-2011, 09:45 PM   #29
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Quote:
Originally Posted by 254S197
A vacuum leak will cause idle surge. The iac is fine.
My idle sits right at 1100 rpms. It has no surge. The iac has 13.4volts at all times. It never changes. What I'm asking is. Should the iac try and close even if there is a vacuum leak?
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Old 06-07-2011, 09:51 PM   #30
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The iac is always open. It's just a metered air leak. If it does the surge when the accelerator is released then there's a problem with the dash pot function. Sen me the year and engine displacement and I'll get you the tech information and diagnosis steps for it.
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Old 06-07-2011, 09:55 PM   #31
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Quote:
Originally Posted by 254S197
The iac is always open. It's just a metered air leak. If it does the surge when the accelerator is released then there's a problem with the dash pot function. Sen me the year and engine displacement and I'll get you the tech information and diagnosis steps for it.
97 cobra with 01 cobra engine in it. 4.6l 4v heads. Did the same thing with my 97 engine in it
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Old 06-07-2011, 10:00 PM   #32
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Cobra ECM?
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Old 06-07-2011, 10:01 PM   #33
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Originally Posted by 254S197
Cobra ECM?
97 cobra PCM with a SCT tuner on it. I can remove the tuner and it doesn't change the idle.
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Old 06-07-2011, 10:08 PM   #34
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Ok so it still thinks it's a 97. No biggie. Just need to know to get the right steps. Is there any fault codes? Or has there been?
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Old 06-07-2011, 10:11 PM   #35
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Quote:
Originally Posted by 254S197
Ok so it still thinks it's a 97. No biggie. Just need to know to get the right steps. Is there any fault codes? Or has there been?
Iac circuit high.
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