I have a 1985 Toyota 4runner with an A340H aisin automatic transmission that is experiencing the following problem with 3rd to OD shifting:
The transmission has a tendency to shift quickly into OD from 3rd and often seems to skip over 3rd entirely.
This occurs at all operating temperatures (i.e. even at cold start), whether or not the OD button is depressed.
In addition, when downshifting from OD to 3rd, the transmission will not stay in 3rd for more than just a second or two. Instead it will shift back to OD or downshift all the way to 2nd.
I did the mechanical shift test (with ECT disconnected) and the transmission behaves as it should (L=1st, 2=3rd, D=OD)
I tried swapping the ECT with one that I know to be good, but that made no difference, I also replaced the solenoids and filter, and adjusted the throttle cable linkage with no change in symptoms.
I'm now considering tearing into the transmission itself and was wondering if anyone has a guess as to what the problem might be?