I hate these types of problems, TPS.... could be.
At least you give a lot of information, unlike a lot of people who post and are so vague and clueless.
Messing with the idle speed control screw should not cause a TPS code.
It may be your TPS, as this feeds to the ECM and the ECM feeds the TCM which determines how your trans shifts. On my 93 TSI, besides a TPS it also has a closed throttle position switch that tells the computer when the throttle is closed and if this is out of adjustment, it causes problems too. I do not know if your vehicle has a separate one or if it is integral with the TPS. Maybe that was the other code???
Otherwise, a bad wire or bad ground and as you are an "ex" mechanic, you know the joys of trying to find that!!