Audi Repair Questions? Ask a Mechanic for Answers ASAP
Any indication that there are faults stored (check engine light on?)
Is the problem with Sport mode, or are you trying to use the Tiptronic gate to manually shift? The Sport mode just holds shifts longer, allowing you to rev higher before upshifting, but makes for slightly harsher shifts. Is this the mode you are trying to use?
Are you able to shift into the Tiptronic gate as well, and use the + and - to shift up and down? I have seen a lot of issues where foreign material (or spilled soda) gets into the protective plastic shields that slide with the shifter, and stick, causing shifting issues or even damage to the Tiptronic gate magnets. If there are sticking issues, you will have to remove the center console around the shifter in order to remove and either clean or replace the shifter cover piece, depending on situation.
So it is able to stay in place in the Tiptronic, but in the Sport it drops back to Drive? I would watch the trim rubber strip for any sign of binding when you drive next, but worst case scenario is that you may have to change out the shifter assembly (the part in the car, not the cables or the transmission) It has detent built into it which may be worn, especially if you always use it in S or Tip.
So it will stay in position in the Tiptronic gate? It's not necessarily difficult to replace the shifter, more a matter of disassembling the cent r console and being able to refit it smoothly- which can be kind of fiddly. The shifter unbolts and the cable disconnects from it easily enough.
If you never drive in Sport, why does it matter? If it will stay in the normal drive position, or Tiptronic which you prefer- but I understand about having a system that SHOULD work and does not. It's up to you to make the decision on whether it is worth fixing or not.
Yes, it would be the shifter assembly.