audi a4 starting problems?

[paul s]

Hi I have a 1998 audi a4 which starts fine when cold, however once the engine is hot, it is ok to stop the engine and restart, but if it is left for 5 mins or so it is difficult to restart. It also seems to be ok after 10 - 15 mins . the engine is a 1.8 turbo petrol. all suggestions welcomed