1993 Ford Taurus Ford Taurus transmission

[quote:ff419e6c86="Matthew1"]Transmission problem
1993 Ford Taurus 6 cyl Two Wheel Drive Automatic 108,00 miles

Transmission shifts back and forth from overdrive to 3 rd. If I leave the car in drive it shifts back and forth from 3rd to 2nd the back to 3rd and so on. P.S. I just replaced a short vacuum tube coming off the pcv valve about a week ago which seem to be about the time the trouble started with the transmission.[/quote:ff419e6c86]

Are there any other symptoms that also appeared around the same time? Such as the "check engine" light? Among the many things that can cause your problem are:

1) bad or "noisy" throttle position sensor.
2) speed sensor(s)
3) bad or out of adjustment MLPS switch (manual lever position sensor)
4) internal electronics - shift solenoids, electronic pressure regulator, etc.

These are just a few.......

Start by having the system checked for trouble codes.