nOw not sure if its right, (it does not sound right to me) but i read a post where someone reckons if you move the throttle body by had, eg while trying to clean it, you can damage the stepper motor.
Anychance someone knacked it trying to sort it out?
Maybe one of the techs at Abtech swapped it out for one of theirs! Seems odd it worked ok befroe it went in and dd not work ok afterwards.
I am amazed they did not find this with a Vagcom log while drivign it would Pretty sure it would have been massively obvious if the tps and body were not moving properly!