03 Gt Woes

Discussion in '1996 - 2004 SN95 Mustang -General/Talk-' started by adamv7010, Mar 8, 2014.

  1. 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.


  2. 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.
  3. No codes. No misfire data...no misfires...according to the ecm at least.

    Plugs are new.
  4. 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
  5. +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.
  6. 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
  7. 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.