My A6 overheated recently so I went ahead and replaced the thermostat because it appeared that the fluid was not circulating. Along with the therm I replaced the water pump, timing belt, serpentine, the whole 9 yards. After getting the car back together it started right up but still got warm so I replaced the temp sensor just aft of the right head. It ran great after that, nice and cool. I drove it to work the next day and everything was fine. My daughter drove it that weekend and it stalled on her, I went to pick her up and it still wouldn't start. The next morning I went to check on it and it started right up so she drove it to a gas station since it was low on gas. After filling it, it would not start again. We pushed it away from the pump into a parking spot and I popped the hood looking for some loose connection but couldn't find any. She tried it again and it started right up. The only thing I can consistently say that I have noticed is that when it fails to start I don't hear the normal click and hum up near the front of the intake/throttle body that I normally hear when it does start. One thought I have is that water got into something when I washed the engine down after replacing the cooling system components.

Any help or other thoughts would be greatly appreciated.
JD