Automatic Transmission May Not Shift Correctly at High Mileages on Geo Prizm

Problem Description and Possible Solution

At higher mileages, (125,000-150,000) the automatic transmission may not shift correctly. This can be caused by the throttle position sensor being out of adjustment or a shift solenoid needing to be replaced. Typically the transmission does not need to be completely overhauled.

Problem Data
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Average mileage: 159,410 (113,674–225,200)
8 model years affected: 1990, 1991, 1992, 1993, more1994, 1995, 1996, 1997
26 people reported this problem
Viewing 1 - 10 of 10 comments
On a cold start, the car won't shift into high gears until it has warmed up. My driving is all highway and I'll be cruising at 65 mph in 3rd gear. I can barely hear myself think until it suddenly decides that it should sift.
I haven't had it fixed as I've already ordered a new car and don't want to be putting money into this.
Doesn't want to shift when cold. Used to be just over drive, now it's all gears.
Stays in 1st gear for half a block. Takes 2-3 miles to shift into overdrive.
transmission is an automatic. on the highway, it runs along at 60 MPH in 3rd gear at 3000 rpm, and when I start up a hill, it shifts into fourth, as soon as I head back down the hill, it drops back into third. As this problems persists, my mileage has dropped about 15%, from 38 on the highway down to about 31.
same problem, will not shift until it warms up to operating temperature
shifted like a stick shift from 1st to 2nd.
When cold and sometimes not the car will not sift correctly.
If I don't let my GEO run for 10 to 15 min when I first start it up, at 7 to 9 miles out the car will go from 55 mph to 45. its right there you can hear the car go to 3rd gear. don't know how many rpm's but it is very loud. then after about 2 or 4 miles afterward you can hear the car go back to normal. I can do this in 90 degree days or in freezing weather. as long as the car keeps running, its fine. if I stop for 10 min. the whole cycle starts again.
my mechanic changed the master brake cylinder but it was a guess. it seemed ok for about a month then started up again. when I push the brake pedal when there is a problem, its as hard as a rock. when the car is running fine the brake pedal works like a normal pedal.
can the car shift from overdrive to 3rd gear?
the car had a high idle. I let the car coast when I was having this problem. I started at 20 mph and let it coast. the car stopped at around 100 yds. I think its coming to the end of its time. this was my best car by far.
My car can't even pick up the second shift!:-/
Major forward gears slipping. Reverse ok.
unless at operating temp the trans does not shift into overdrive, throwing dtc, shift solenoid E