This is a fantastic post, I hope someone can see this and gets a moment to reply. I drive a B8 A4 '09 just like this one. I'm dealing with the same exact symptoms, had the sensor replaced and the car seemed to only get worse. It still turns on but only after turning over for what feels like a good 4-5 seconds. and now when i drove it home it was intermittently bogging down to the point it felt like its ready to cut off.

I am being recommended by 2 different mechanics to replace the crankshaft itself. However, after reading this and how it could be the timing chain/tensioner I am unsure how to proceed. I would take it to Audi if I wasn't so certain they'd find a way to certainly rape me and the information I am getting back from both these trusted mechanics is at least reliable enough for me to make a proper decision but before all that I wanna see what the Audi community has to say.