A3 starting probs

Hi, I bought a 57plate A3 2.0tdi S Line about 6 weeks ago, but im having probs with it starting, its not everytime and seems a bit random, it'll turn over but not fire up, took it to audi yesterday and they said it came up with the fault code for the crank shaft position sensor, after looking at it they reckon it had a bad connection which theyve fixed but have ordered me the part anyway, the guy was convinced the car would be fine though... well guess what... got 2 mile down the road and it did it again!! it seems more when the car is warm.
Im now not convinced this is the prob has anyone else had similar probs??