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Intermittent engine and tranmission problems (see details)

I got a 94 Ford Mustang 3.8L V6 Automatic with 217,000 miles that has intermittent problems. The engines rpms periodically bounce up and down between 500 and 1000 rpms as I sit in ideal. The transmission starts to almost lose its mind sometimes as it will shift up and then down and then slam back into the right gear. It will do this without any chance in incline, speed, or application of the gas pedal. It will do this just as I’m coasting. Both of these problems started at around the same time, and have progressively gotten worse, so it seems these problems are being caused by the same problem. It acts up worst when its hot out, or when I’ve driven the car for a while on a long trip, it then starts to act up.

I’m actually one of those car care-takers that is pretty methodical with my routine maintenance. I change the oil and filter every 2-3,000 miles, fuel filter every 9-16,000, spark plugs every 24,000 miles, have replaced the plug wires not too long ago, flush and change the filter in the transmission every 33,000 miles. I already rebuilt the transmission just 70,000 miles ago, and changed the fluid only a few thousand miles ago. Just by the nature of the cars activity (as over 100,000 miles of owning the car, I’ve experienced mechanical failures and electrical failures), the behavior of the car really feels like an electrical issue, just by the feel of the car when the problems occur and the behavior of it.

I was advised about a potential electrical problem by Ford where they detected at 177,000 miles via PID scan that voltage had spikes as low as 0.012 volts, and they weren’t sure what it could be. They said whatever it was should have been addressed, as those spikes would have played havoc with my computer. Since then, I replaced the alternator, and I also found my one-touch window module had fallen off the interior door panel into the bottom of my door interior, and got soaked with water and was fried, so I replaced that as well as well as the window motor as the diode had been worn through the window motor due to the one-touch window module being fried. I really want try and see if I can address this before Christmas, as I live in Pittsburgh and I’m trying to drive to Maine to visit my mom for the holidays. And the last time I tried to make it to Maine I had to turn around because the transmission was acting crazy with the shifting of the gears (as I’ve said before, when I take long trips is when it will start acting up) Any input or advice?

There may be some valves sticking inside the transmission and using a product called Trans-X may help. As fas as the low voltage spikes go that amount of voltage is insignificant. It is just noise in the power bus. I wouldn’t be concerned unless it goes higher than a half of a volt. Usually bad grounding is the cause of noise problems unless the alternator is bad.