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Car's running poorly (see details)

I have a 94 Ford Mustang V6 3.8L Automatic AODE. The car as a whole is not running optimum. It has 217,000 miles on it, and it starts acting up after I’ve driven it for a while especially, but the tranmission will start shifting around erratically, and if I punch the gas, the shift in gear sometimes is way late. Also I’ve noticed that while the car ideals, the rpms fluctuates sometimes. The rpm indicator will bounce up and down 500-1000 rpms like the car wants to die. I was thinking maybe the computer is possibly on its way out (it’s the original computer in the car). Any ideas?

For the bouncing idle speed (clearly it is not ideal), look for a disconnected or cracked vacuum hose.

As to the overall performance of the car, the best way to begin it to bring the car up to date with ALL of its maintenance. Spark plugs and plug wires are the most likely culprits, but if the air filter and fuel filter haven’t been changed in the past 3 years, those should be replaced.

With over 200k on the odometer, it is likely that your transmission has just plain worn out internally. You might want to try a fluid and filter change, but don’t expect any miracles–especially if the fluid and filter were not changed about 5 times previously over the life of the car.

Check the vacuum.

17 years old, a 3.8 and a poorly designed trans??? Get another vehicle.

The idle problem could be due to a vacuum leak as mentioned or a faulty Idle Air Control valve. The IAC is an air leak also although it’s a computer controlled one.

As to the transmission you have not provided any info about this transmission; mainly as to whether it’s ever even had the fluid/filter changed. If not, you can try that for a start and scan the car for codes.
At 217,000 miles and 17 years of age a transmission problem is not necessarily out of line, especially if it has not been serviced regularly.

The odds of this being a faulty computer is near zero in my opinion.

I’m pretty methodical with my maintenance. I ensure the fuel filter and air filters are changed at their regulator intervals (9,000-16,000 miles, spark plugs every 24,000, and I think air filter is 30,000 right? Either way the air filter I know is not due for a while, I’d have to check my maintenance sheet.) The transmission was rebuilt only about 60,000 miles ago, and they replaced everything including the valve case. I flush the transmission every 33,000 miles as well. I just had the transmission flushed and filter replaced a few thousand miles ago (but it was acting up prior to that, and the flush and filter replacement has seemed to have no effect on it)

I also had a problem with my electrical system previously. Ford 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 havic 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. I’ve replaced those two things. and ensured there are no diodes that are worn through. Could this give any insight into what this problem might be?

I’m pretty methodical with my maintenance. I ensure the fuel filter and air filters are changed at their regulator intervals (9,000-16,000 miles, spark plugs every 24,000, and I think air filter is 30,000 right? Either way the air filter I know is not due for a while, I’d have to check my maintenance sheet.) The transmission was rebuilt only about 60,000 miles ago, and they replaced everything including the valve case. I flush the transmission every 33,000 miles as well. I just had the transmission flushed and filter replaced a few thousand miles ago (but it was acting up prior to that, and the flush and filter replacement has seemed to have no effect on it)

I also had a problem with my electrical system previously. Ford 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 havic 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. I’ve replaced those two things. and ensured there are no diodes that are worn through. Could this give any insight into what this problem might be?