I'm helping my 16 year old son work on his second car (first is a 1970's Bradley GT)

He bought a 1997 960 wagon for $600 knowing it would need some work. when we test drove it it ran a little rough but nothing that scared me off, but we got the price reduced due to the up arrow and lights flashing on the ESW switch. we did some research and were fixing and tinkering as he came up with money. we replaced the pnp switch and symptoms didn't change. we checked and cleaned all electrical connections on drivers side of tranny. no change. Swapped in a new used TCM and it all went away. the car idles smooth as can be. next he changed spark plugs and saved up for new tires. when we went to pull it out of the garage 3 days later runs really rich and up arrow and flashing ESW back on. suggestions on next step. I'd like him to stay engages and excited about this project and need help maybe pinpointing rather than just throwing out fixes as he can afford them,

thanks in advance

I have had two 960s that have intermittently exhibited those symptoms. Moisture and sudden temperature changes seemed t bring it on sometimes. The one thing that seems to cure it the most was simply time. Eventually the flashing ESW would stop, and everything would be fine for months. I rather think that whatever was wet, like the multipin connector on the side of the tranny, would dry out. I tried all the solutions you have, as well as others that are suggested in the FAQ.
Good luck
JD

I would see if you can get any fault codes. Have you changed the trany fluid and filter. The esw switch get another one from pick and pull and try it, if not at least pull the old one out unplug it and put back in to clean the connection., and try and clean it.