hi there, i have a 2002 a4 2.5tdi. iv owned it for 2 years and its always had trouble starting if i park it facing down hill. if i leave it parked facing down hill for 10 mins it will take maybe 3 attempts to start, or if i leave it over night it takes around 20-25.(in other words a long time) also if there is more than half a tank of fuel it will start fine. and on flat or facing uphill it always starts no trouble at all. my friend is a mechanic for a maiin audi dealership and nobody has any idea what it could be, he also plugged the computer to it and it came up with no problems. if anyone could help it would be much appreciated, many thanks