1993 Ford Escort idle control valve

My car wouldn't shift out of first gear, it would also down shift when idling in between 3rd and 4th, all the way back down to first gear, the FUEL CUTOFF light would come on along with the check engine light and it would die out once the car stopped.

Then if I restarted it would act fine again, I replaced the Idle control valve, then in the first 24 hrs it would rev high when I let off the gas at any speed, the following day it would rev low when letting off the gas. Then after a 20 min dirve to Wal-Mart and a 20 min shopping I went to start it and it immediately gave those errors and symptoms of not shifting out of first gear

I crawled it to a friends house sat for many hrs restarted and it was fine again 20 min drive.

Questions;
can exhaust leaks affect this?
is this a 'brain box' or I guess they are called ECU issue if so how to check it?
there is a dial on the side of the idle control unit, a websearch pic shows it too, does that adjust anything? It doesn't seem to adjust it?
Should I adjust the idle speed? It idled higher with the new unit? (Its adjusted by a cable, weird system)

Im going to bring it to a shop for muffler patches and don't want to be ripped off since the shop sells used cars too, please help thanks