I have a strange problem with my 1996 Ford Mustang GT 4.6.

When I put it in park, the engine will drop below 500 RPM and will usually die. If the engine doesn't die it will return to normal RPM. I don't know if it is related or how it could be, but I just repaired the fuel filler tube that was leaking badly. The problem started after that repair was made. I haven't been able to check the codes because my son has the car at school.

Does anyone have any ideas why this would be happening?

Thanks to all who reply

  • Does this only happen if you put the car in to Park and not neutral?
    – rana
    Jan 16, 2017 at 17:10
  • Yes, it only happens when it is put into park. Neutral is fine.
    – user25200
    Jan 18, 2017 at 2:03
  • Can the neutral safety switch cause stalling? The neutral safety switch has been out of (adjustment?) for a while.
    – user25200
    Jan 18, 2017 at 2:13
  • Correction: It does drop in RPM when it is shifted into neutral just the same as park. All other shifts are fine, It does not die as much as it was before, but the RPM is still dropping to near stall and then returning to normal RPM when I shift to park or neutral.
    – user25200
    Jan 21, 2017 at 22:54

3 Answers 3


Resolved:) The transmission fluid was low...It took almost 2 quarts to fill it up. I used the opportunity to add some Lucas Transmission Fix and every thing seems fine now.


From the symptoms and the timing of it happening after the fuel neck repair, my first guess would be during the repair a fuel-related vacuum leak of some sort was created, maybe a hose came loose during the repair, possibly at evap cannister or vapor purge valve.

  • I will be sure to check that out. I was able to make the repair with out dropping the gas tank and the fuel neck vent is inside the fuel neck on that car so I don't remember disturbing vacuum lines...but I also replaced some brake lines and replaced an axle seal...so I did do some banging around back there. It sounds possible. Thanks, I won't be able to look at it till next weekend. Until then I will check out online what the evap system looks like on that car
    – user25200
    Jan 17, 2017 at 4:05

I would try cleaning the throttle body and idle air control valve.

  • It would be helpful to explain why you think the throttle body and IACV should be cleaned
    – Zaid
    Jan 16, 2017 at 16:50

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