04 Gt Rough Idle. Out Of Ideas...

Discussion in 'SN95 4.6L Mustang Tech' started by richy28510, May 25, 2013.

  1. I recently pusrchased a 04 stang. After a few days it developed a slight rough idle. It has gotten worse and worse, but does not throw a code. I've replaced plugs, air filter, fuel filter, pcv valve, upstream 02 sensors. . I cleaned the throttle body and injectors. I unplugged the maf while it was runnng and idle smoothed out and it ran amazing. So I figured maf was bad got new one installed and same thing. I reset the computer a few times. Nothing is fixing this rough idle any suggestions???
    04 ,72k miles.
  2. Check the fuel rail pressure sensor. You can pull the vacuum line off and if it squirts fuel at you, then it is bad.


    Look toward the firewall on the drivers side.
  3. I will check it. Thanks
  4. You may want to check your idle air control valve. When my idle got rough, I replaced it and it took care of the problem. It is a fairly common problem with Mustangs.
  5. Tnyway to test if it id bad?
  6. Stupid tablet...Anyway to test it?
  7. I think there is a voltage test. It's in a Chilton's. Go get one...best 25 bucks I ever spent.

    Generally with a bad IAC the car will not run without mashing the gas. Keeping the RPM's up will allow it to run but as soon as you let off the car will die. I've never heard of any rough running issues with the IAC but that doesn't mean it doesn't happen.

    The Fuel Rail sensor is an easy one. Once you pull the vacuum line you will know it there is a problem.
  8. Check the fuel rail sensor working properly.
  9. Hopefully when I get my sct itsx tuner Monday I can map the idle to see whats going on.
  10. It may tell you something, then it may not. Is it throwing any codes?
  11. Might be a vacuum leak. Check all the lines and hoses for cracks.
  12. If you can have the ECU read for TIDs you might find something useful. My dad's Mustang had issues and I found it was failing TIDs relating to the DPFE but it wasn't throwing codes. I checked and the DPFE hoses were bad and causing a vacuum leak. Car idles great now. Not saying that is your problem.

    As far as the IAC is concerned, it wouldn't hurt to yank it out and clean it.

    If you are worried about a vacuum leak you can take it to a mechanic and pay for a smoke test.
  13. Just installed my tuner and ran it and blam at 80 it broke up and threw a code. Bad coil. But I think I have more issues than that. Will check vacuum lines
  14. Found out car sat up for 3 years.
  15. The TIDs would have told you about a missfire on the cylinder without it throwing a code. You may or may not have a bad coil. Could also be the spark plug or the injector. Move the coil pack to another cylinder and read the TIDs after you have the issue again. You should see the missfire count in the TID follow the coil pack. If not you have another problem.
  16. Somehow the coil connector unplugged itself . Replugged and it sounded like it (normal self) ses light went off. I will have the car at the shop tomorrow to test your idea.