I have an intermittent and recurring issue with my 2012 S5 4.2L where it occasionally seems to lurch and run rough at low speed (40-50 KPH) in 2nd/3rd gear and hesitate badly upon acceleration with the EPC light illuminating. This problem has seems to arise when the vehicle hasn’t been used for a period of a few weeks and while it the engine is still fairly cold after only 10-15 minutes of starting it up and driving around in town.

the vehicle has been to my local Audi dealer twice; each time with them detecting a low fuel rail pressure fault, but their diagnostic hasn’t pointed to any repair because the vehicle seemed to be running fine by the time I got it to the dealer. The diagnostics have revealed a P129B fuel pressure regulator valve bank 2 open circuit and a P0332 knock sensor 2 circuit low input with a possible N402 valve issue, but the fuel rail pressure was reading OK via MVB and there were no leaks at the fuel pump connector.

had anyone else encountered this issue and solved it? I realize that the hesitating upon acceleration is a built in safety feature to limit the engine when this fault it detected, but need to get to the bottom of what is causing the fault. Intuitively, it feels like a fuel pump or fuel filter issue, but the dealer says they are hesitant to replace either because they say the fuel pump and filter are integral to the fuel tank in my S5 making it is time and cost intensive repair. I also wonder if it is a consequence of the fuel being old/stale or contaminated with condensation because I use the vehicle very infrequently.

I would love to hear from anyone with advice on how to address this and what the possible cause is. I need to get my dealer to do a comprehensive repair rather than just erasing the fault code and telling me to monitor the vehicle...