First post, sorry if it's lengthy or a bit incorrect.
About 6 months ago I bought a 94 automatic 4 cylinder, shows 344k but 130k on the motor. Ran awesome until a month or so ago. I was driving downtown doing 15ish mph, the car lost acceleration and the D4 light started blinking. I pulled into a parking lot and sat with it in P. While sitting there the shifter began to click like it was trying to change gear. I cut the car off and waited about 15 mins, turned it over and it ran fine--no D4 light. The next day I had the same issue. I immediately pulled over and let it sit in P for a few minutes and it was fine. I made sure fluids were good, ect.
Everything was fine until last week. The same issue again but when I parked the car it locked into P and I couldn't change gears. After waited 15 mins. I used the key release to get it into N, started, and shifted to R (reverse was fine). But when I put it in D4, or any forward gear, I couldn't really accelerate. I limped home doing 20mph at 2k rmps. It sat 3 days until someone had time to look at it and when I went to see if I could get it to go in N to be towed, D4 was off and it shifted fine. They looked at it and said it could be the tcm, or a short from the battery that was causing the tcm to try and reset while driving. But they couldn't be sure unless they could get it while it was happening.
Today it was fine until I stopped to check my mail and got back in the car to find it locked in P again but no D4 flashing. I used the key release to unstick it and get it up my drive. Parked and checked and it was locked again. I checked it 10 mins later and it was fine. The check engine light has never come on.
Any help on what the issue could be would be hugely appreciated.

 

The locked shift is either brake light switch is open, the shift lock solenoid is misadjusted or failed.

Check brake lights w/ brake pedal pushed. If no brake lights then you have a damaged switch. Sometimes they can be fixed by dousing liberally w/ WD40 and manually excercising the switch.

Shift lock solenoid will require removing the center console to access and inspect. You should be able to hear the solenoid (if its working), when brake pedal is pressed,...and if you listen very carefully!

D4 light flashing is probably unrelated to shift lock. Go to DIY forum and see how to check for flash codes. Check Engine and D4 flash codes are same procedure and code; long flash =10 and short flash=1. If multiple codes are present they are separated by long pause (2-3 secs).

good luck