You've gotta watch wheel speeds while driving. This requires VCDS and a portable computer, even a good shop probably won't have this unless they do a lot of VW/Audi work.
Each wheel has its own speed signal. One of the four is not like the other three, and it very well may not set a fault code. Once you find the oddball wheel, visually inspect the sensor, wiring, and tone ring. If all passes the visual check, replace that sensor.
You're never going to be able to fix this without VCDS though. Generic OBDII is of no use here.
Re-evaluate the hard pedal after the ABS issue is fixed.