My 97 (2.5 L, auto) has transmission problems when driven long distances. After about 40-60 miles, it starts flashing the overdrive light and cruising RPM climbs by 500-1500 from the normal level, and fluctuates. Once it starts doing this, if I turn the car off for a brief time and then run it again, it will maintian the expected RPM to speed ratio more of the time, but still won't do it consistently, and the 1-2 shift is very harsh.
Frequent hills, headwinds, or higher speed will make this problem crop up sooner.
I think that the transmission is more prone now to unlocking the torque converter under load than it was when the car was newer. I'm not terribly sure about this because if it is different it changed gradually, but it does seem to downshift sooner than I expect, even when cold.
Now for the good part, in which I do foolish things. I took it to Aamco to have them look at it several months ago. They rebuilt the transmission at considerable expense and delay, but it fails exactly the same as it did before. Aamco then claimed that the problem was not in the transmission, and started looking for other "problems" to blame. I had a longstanding CEL condition (bad cat, p0420), which they decided was the root cause of the transmission problem. They wanted a few hundred bucks to rebuild the intakes, claiming those were leaking, which caused the cat error, which caused the transmission to fail. I decided I'd had enough of their help, and have since resolved the cat issue and a few other related engine problems. Of course, the transmission still has the same problem that inspired me to take it in in the first place.
Can anyone provide any advice as to what is actually going wrong in the transmission?
I have some memory of a post here some years ago about a problem where valve wear causes a reduction in the efficiency of the transmission oil cooler on these cars, which in turn results in more rapid valve wear. I seem to remember that the symptoms were overheating transmissions and the inability to keep the torque converter locked. I now can't find this post, so I may just be imagining it.
Anyway, thanks for any thoughts you might have.
