03 Gt Woes

Discussion in '1996 - 2004 SN95 Mustang -General/Talk-' started by adamv7010, Mar 9, 2014.


  1. adamv7010

    adamv7010 Member

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    Recently got into mustangs...but not to automotive performance.

    Recently bought an 03 gt with a leaking intake manifold...

    I replaced that with a new frpp manifold.

    Before the swap I had a condition where it would stumble at idle a little, then during wot pulls it would act as if it were starving for fuel.

    I really figured the leak was soaking a plug or two causing a misfire. I blew the plug bores out with air when I had the Mani off and got some liquid out of a couple.

    I put it all back together and everything went smoothly. I replaced the gasket on the IAC simply because the ford store didn't have a valve on the shelf.

    Long story short, with the new intake and dry plugs, I've still got a stumble at idle, which according to my live wire, is around 680-710rpm.

    Anyone wanna guide me to a starting point? Are these 2v coils known for breaking up?

    I have several k$ worth of diagnostic tools, but I don't have an IDS, so I can view most anything, just can't flash.

    Any advice is welcomed.

    Thanks

    Adam
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  2. 1987stangman

    1987stangman Member

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    Codes? Check for them even if no SES light is on. I would replace the plugs First and test. Then start looking at the cops.
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  3. adamv7010

    adamv7010 Member

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    No codes. No misfire data...no misfires...according to the ecm at least.

    Plugs are new.
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  4. jcgafford

    jcgafford Well-Known Member

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    Those 4.6 liters are known for a couple different spots that fray vacuum lines and cause problems like this. Also if the iac is not a fomoco part I bet it is either causing you problems or is about to and it will not throw a code
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  5. Mattstang04

    Mattstang04 Active Member

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    +1. If the IAC isn't a Motorcraft part, these motors tend to reject them. Then after you put a good one back on, it takes a little time for the computer to relearn the new valve.
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  6. adamv7010

    adamv7010 Member

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    It is a fomoco part...how old it is I can't say.

    I do have it running pretty good now. The short eBay cai that the po put on it went away and it got a better one from late model...that made a good bit of difference.

    Cleaning the maf made the most difference however
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  7. jcgafford

    jcgafford Well-Known Member

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    The fomoco iac in my wifes 4.6 was the start of 2 years of problem solving till a replacement fomoco iac totally fixed all symptoms. Ridiculous how badly that stupid little part can screw with that engine.
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