94 Camry shifts to coast jerks back into gear
 

I have 1994 Camry 2.2 w/ auto transmission 151K miles. My problem happens around 35-45 mph. While trying to maintain speed, the car will shift into coast and the RPMs drop under 1k. If you maintain position on the throttle pedal it will spike increase the RPM and then shift hard back into gear. It will continually do this at all conditions during this speed range. The cruise control will not work and I believe this is related to whatever part is causing the shift into coast. Also I have a very long steep downhill on my way to work and if I shift to neutral to coast the transmission will downshift pretty hard before it goes into coast. This happens even if I let it coast before shifting.

My transmission recently went out and I had a used one put in. These problems carried over with the new transmission. Mechanic said he didn't know the cause.

I have seen other users post here with similar symptoms, but I have never seen a solution.

Did you replace the torque converter?

The trans does have its own trouble code readout system.

I don't think it's the transmission because this is the 3rd transmission that has done this. I'm not sure if the TC was replaced. Would that be standard practice? I got a used transmission. I was thinking something like TPS, idle air control valve, crankshaft speed sensor, etc.

TC can cause this issue.