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How To: IAC Rev Mod (Fixing the hanging RPMs)

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Old 10-16-2010, 10:43 AM   #41
GTtony
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I look mine out a couple days ago after a month. I was tired of the horrible noise it made out of my exhaust and my car stalling and turning off randomly.
+1

I did the same as well. I had mine a week or so. It is cool that rpms droped fast, But the HORRIBLE HISSSSSS my car made while i had it in was driving me crazy.

FYI TO ALL: there are TWO other ways of correcting this issue!

1. Change the dashpot settings w/ a tuner.

2. (For 99-04 GT's w/o forced induction only) Purchase the Bullit IAC from your ford dealer $157. it is calibrated for the Bullit Mustang which has a larger CAI than the GT.

I plan on having my sct flip chip re-flashed when i put in LT's, so i'll do it then PEACE.
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Old 02-02-2011, 11:33 AM   #42
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Default rev hanging

Got a wick question. I have a stock 2000 gt. I was wondering do you only drill the side of the of the gasket that is open on the throttle body. Thanks. Guys. Awesome site.
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Old 02-02-2011, 11:54 AM   #43
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Use a 1/2" copper pipe cap in the IAC feed hose--a lot less hassle...
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Old 02-02-2011, 11:57 AM   #44
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That is true. Looks a lot simpler
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Old 02-02-2011, 12:03 PM   #45
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Hey cliffyk. What yr is your car.
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Old 02-02-2011, 02:19 PM   #46
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Hey cliffyk. What yr is your car.
2003, as in my signature--the IAC on your car will be differently shaped, with a vent cap, however it works the same...
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New ride (7/1/2013) 1998 Mercedes SL500-5.0L 32V VVT 326/347 HP/tq


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Old 02-02-2011, 04:13 PM   #47
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I tried changing the gasket size to drop rpm's faster. But my idle is at 1100. I used 3/16. Should I step up another size or go down a size
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Old 02-02-2011, 05:04 PM   #48
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I tried changing the gasket size to drop rpm's faster. But my idle is at 1100. I used 3/16. Should I step up another size or go down a size
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Old 02-02-2011, 05:46 PM   #49
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I tried changing the gasket size to drop rpm's faster. But my idle is at 1100. I used 3/16. Should I step up another size or go down a size
In my experience 3/16" is too small, a sloppy 9/32" or 19/64" seem to work best.

However the 3/16" hole should not make the idle high. Make sure you do not have a vacuum leak at the new gasket--that will make the idle high.
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New ride (7/1/2013) 1998 Mercedes SL500-5.0L 32V VVT 326/347 HP/tq


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Old 02-02-2011, 08:22 PM   #50
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I've been running the copper cap for about three months now and it works well. Don't know what hiss it was causing with you guys. Guess I'm lucky the whine of the blower covers it up...
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Old 02-03-2011, 03:06 PM   #51
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Similar method on a 4v?
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Old 02-03-2011, 04:36 PM   #52
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Put original gasket back on iac and put In copper cap instead. Rpms are still 1000-1100. I used a 3/16 hole an suggestions
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Old 02-03-2011, 05:02 PM   #53
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Put original gasket back on iac and put In copper cap instead. Rpms are still 1000-1100. I used a 3/16 hole an suggestions
Disconnect the battery for 5-7 minutes to clear the KAM, this will force the PCM to relearn the idle air trim values--if the idle is still high then the IAC may be bad.

Test the voltage at the red wire of the connector, unplugged from the IAC with the key in RUN and the engine off, it should be 10.5V or better--if it isn't you have a wiring problem;

Test the coil resistance of the IAC, it should be 6 to 13Ω, if not the IAC is bad--replace it;

Test the resistance of each IAC terminal to the IAC body, it should be >10kΩ, if not the IAC is bad, replace it.
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SOLD! - 2003 GT, UPR X, FRPP 24lb/h, Magnaflow, PP 70mm TB & plenum,
Delta Force tuned, Steeda UDPs, Ralco flywheel,
RAM HDX clutch, 3.73s, 262 rwHP/305 lb-ft.

New ride (7/1/2013) 1998 Mercedes SL500-5.0L 32V VVT 326/347 HP/tq


Engineering is, at its base, making what you want from what you have.
At its extreme it is making what you want from what you can get.
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Old 02-03-2011, 05:39 PM   #54
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I just got my first mustang not long ago and have always hated the rpm hang. luckily i found this forum. Just did this mod. It was so easy. And now the car works so much better. I saved my old gasket just incase I dont pass emissions check. Thanks for the awesome write up.
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Old 02-03-2011, 06:31 PM   #55
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Its running better now. Drove home from work and seems to have reset itself. Staying close to 850-900 rpm. Thanks for all the help guys.
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Old 02-05-2011, 12:31 AM   #56
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Hey guys. I got a problem with my 2000 gt. I did the iac mod with the copper pipe cap 3/16 inch. Now. When I go to put fuel in my car it starts dropping idle. As I am putting fuel down gas line the car will idle crazy then shut off. And the gas hose will click off like it's full of fuel. When it clicks off I can hear something like air pressure being released inside the tank
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Old 02-05-2011, 07:41 AM   #57
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well how does the car react when you add the gas the "normal way" with the car turned off? LOL
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Old 02-05-2011, 08:57 AM   #58
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I have always left them running lol. It just started acting strange tho. I can turn it off and it does the same thing. It's like there is pressure built up in the tank. Or something
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Old 02-05-2011, 09:15 AM   #59
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I have always left them running lol. It just started acting strange tho. I can turn it off and it does the same thing. It's like there is pressure built up in the tank. Or something
I was going to comment, however my mother always said if you cannot say something nice, say nothing...
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SOLD! - 2003 GT, UPR X, FRPP 24lb/h, Magnaflow, PP 70mm TB & plenum,
Delta Force tuned, Steeda UDPs, Ralco flywheel,
RAM HDX clutch, 3.73s, 262 rwHP/305 lb-ft.

New ride (7/1/2013) 1998 Mercedes SL500-5.0L 32V VVT 326/347 HP/tq


Engineering is, at its base, making what you want from what you have.
At its extreme it is making what you want from what you can get.
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Old 02-05-2011, 09:24 AM   #60
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What's the problem with leaving one running while you refuel. Any ideas on whats wrong with my car thanks
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Old 02-05-2011, 09:24 AM
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50, cleaning, directions, gargle, gt, hang, hanging, hard, iac, installation, mustang, rev, revs, rpms, shifts, start

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