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I am having a rather interesting problem that I can't figure out with my 1996 3.8L v6 with 137k on it.

Occasionally, I will experience a problem when I slow down or stop the car just gives out and shuts off. I can kind of tell that this is going to happen ahead of time because when I step on the gas I will have a bit more power than usual (I'd be going at like 30-35 mph at this point, tap the gas and the car will power forward) then when I go to slow down/stop the RPMs will drop below 1k and give out. This will happen about once a day after the car gets warmed up, it will start again immediately without any trouble or hesitation.

Car has an aftermarket cold air intake, throttle body, plug wires and distributor.

Recently put in a new MAF, new TPS, new IAC, and a new PCV Valve. I did this when I installed the cold air intake and throttle body to clear a too lean code as well as idle issues I was having, it did the trick on that.

My next thought was to try the fuel filter?

Can't really find many other threads that contain an issue like this one, seems like a one off to me.

Does anyone have any insight?

Thanks!

EDIT: Additional Information: I can smell a strong gas/exhaust smell coming into the cabin right before the car is about to stall when I let off the throttle.

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Amelio: You can try changing the ignition coil and the spark plugs. I had a similar issue a few days ago, and we found out that the ignition coil had one bad terminal, and the spark plug located in that terminal, was a little wet... Give it a try! I'm a Ford Mustang 2004 v6 3.8L owner from El Salvador..

  • After having a ford mechanic stair at it and try a multitude of things, it finally clicked. The person who wired up the coil wired the plug wires perfectly backwards. This caused only the lean/rich codes to be thrown and the PCU to have no idea what was going on. The cylinders were firing in the correct order...reversed. A very interesting problem. But your answer was the closest. :) – Amelio Wright Jul 8 '15 at 13:20
  • Also, the car also had spark plugs with 4 electrodes on each installed. That seemingly did not help the situation either. – Amelio Wright Jul 8 '15 at 13:31
  • Amelio, is always useful to replace once in a lifetime the wiring as well... I had 11 years old spark plug wiring, and now, after the wiring replacement, there is a huge improvement in motor power and gas saving... – Joel Hernandez Jul 8 '15 at 14:14
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Plug an ODB2 reader and check for any fault codes. Might be related to the coils/plugs like Joel said, could also be a fuel trim issue caused by bad O2 sensors. An ODB2 reader would let you check all of this.

Could just be the idle valve on the Throttle body. Do you still have the stock TB? Would be worth a try to swap them. If not, make sure it's clean.

  • The fuel trim levels did play a part, and I did end up doing a new fuel pump and sender because of that. The biggest issue was in the coil wiring itself. Throughout the troubleshooting process, I noticed that I could never get the fuel trim levels to sit in the correct range. The odd thing was was that when I let off the throttle while measuring fuel trim, the pressure actually increased, but while on the throttle, it decreased. Strangest thing ever. But the correct coil wiring and new fuel pump fixed the trim issues. – Amelio Wright Jul 8 '15 at 13:26
  • Hey, good to know and I'm glad you found what was wrong! Indeed tricky... – Capsule Jul 8 '15 at 13:41
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The nature of your problem suggests a vacuum leak and the gas smell suggests an evaporative emissions control (EVAP) leak. Might be worth a check.

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