2003 Gt Rough Idle When Out Of Gear

Discussion in 'SN95 4.6L Mustang Tech' started by Snoopius, Jul 23, 2013.

  1. Hey guys,

    I've been chasing a very slight idle issue that only happens when I'm in neutral/out of gear (5spd car)
    It's only about a 50-100 rpm change, but enough to tell something's up and shake me inside the car

    Here's what I've done so far;

    Replaced all 8 plugs
    Replaced fuel filter
    Replaced TPS
    Replaced alternator (battery tested ok)
    Replaced MAF
    Checked PCV (it does rattle, and has suction, I also get suction through the oil filler with the cap off)
    Unplugged IAC and car does die, have also cleaned it (there's a new one sitting at Advance for me otherwise)
    Checked for vacuum leaks with MAF cleaner spray

    Here's also some datalogging values;

    [email protected] .56 @1500 .61
    LFT1 @idle .97 @1500 1.00
    LFT2 @idle .96 @1500 1.00
    MAFV @idle 185 @1500 230
    ^CTS @idle 470 @1500 No Change
    TPV @idle 184 @1500 199

    I wouldn't think it's a C.O.P. or injector thing because I feel like that would be more obvious and not just at idle, I also have been told if it was an O2 thing my LFT values would be out of whack.

    Any help is appreciated, I know IAC is the big one on these cars, but just because I've cleaned it and it kills the car when unplugged I assumed it was doing fine...

    Thanks in advance!

  2. I don't have any real clue but are your motor and trans mounts in good shape?
  3. You know I've never really looked, I know anything is possible but it's been doing this since it was a 50k car, it really doesn't feel like it's mount related, if it was though would I only notice it at idle like this?
  4. I replaced the IAC the other day, idk what was up it but when I would be going down the road over 2000rpm, it would stick there and wouldn't idle back down, so I cleaned out my stock one and put that back on. Regardless of what was going on there, it had no effect on my actual sitting idle, only other thing I could think of is cleaning my EGR next.
  5. So right now I'm just about out of ideas on this, also almost out of parts to replace!

    The only thing I can think of yet is if my throttle body needs a cleaning, here's my logic on everything else;

    Spark/Electric-Should be good, plugs are new, bad COP should throw a code or be worse than just at idle, alternator is new, battery has proper volts when running and when off
    Fuel-Should be good, fuel trims are good, filter is new, fuel rail and pump voltage/flow is good, injector issue should be worse than just idle
    Air/Vacuum-TPS is new, MAF is new, IAC didn't change with new one (cleaned and reinstalled old one with no change), vacuum leak should mess with fuel trims

    Feel free to point out any errors in my thinking, or if there's anything else for me to try, I do have datalogging capabilities.
  6. I checked my COP boots today, 6 had a few tiny cracks you could see if you squeezed them, 1 had many more and bigger cracks so I replaced that boot, and the last 1 is an Accel coil I bought 2 years ago and under my CAI so I didn't check it, do these tiny cracks make a difference?
  7. Yes, the electrical current will arc to the motor instead of the spark plugs which equals misfire. And it could be just slightly off that it will not throw a code.

  8. View: http://youtu.be/qUcoXGs4ZOI

    This is what I experience, in case anyone thought it was worse than it is, I know it's hard to tell without being in/hearing the car, but this is how much my needle moves (not much at all)