The car: 1991 Jeep Cherokee, 190,000 miles, automatic, 4WD.
The trip: 194 miles from Chicago to Grand Rapids, MI. 14 degrees out.
The problem: 70 miles into the trip, 65 of which are highway, the torque converter unlocks and locks repeatedly for about 10 miles. Stop at the rest stop, shut car off for 5 minutes, proceed. 50 miles later, same thing, but this time it tries shifting into third, then back to fourth, then re-locks. Then unlocks, relocks for a few miles, etc. Then it's fine the rest of the trip.
The work done: Flushed transmission fluid. I figured it couldn't hurt and now I know the last time it's been done. It was orange before the flush.
The result: On the way back today (also 14 degrees out), it does the same thing, only once, after about 100 miles.
The diagnosis: Bad solenoid causing the clutch on the torque converter to unlock and lock randomly, also causing the TCU to think that I'm accelerating when I'm not, hence the downshift.
The question: How close is my diagnosis? Is there any way to test the TCU? And can I get the torque converter solenoid from anywhere other than a dealership?
-moitz- j dot meuzelaar at gmail dot com