Stingray5

I have an A4, 06 plate. It has been resident at Audi Doncaster for about the last seven weeks, due to a starting issue,. If the car is parked facing up hill it simply will not start, it just turns over, even if it does fire, it is extremely lumpy for a few seconds. Once running however, it is fine. Audi cannot seem to fix the problem, they have changed the fuel pump, tandem pump, injectors and are still scratching their heads. (as I am) Is there anyone who has experienced this and managed to solve the problem? If so, what was the cause? I had new head gasket fitted last summer which is roughly when this problem started..... I don't know if this is a clue?