Ive not had this motor very long . turn the key the engine starts then cuts out straight away , after leaving it a little while turn the key and it starts .
and the engine runs a treat . it does,nt mater if the engine is hot or cold the problem is intermittent . any ideas please .

 

When I first brought my car (same as yours but 97 model) 4 years ago I had a similar problem. It was intermittent but got worse. It is some sort of 'linking' between the actual key and a 'stop thief' detection device in the ignition system. My local Audi fixed the issue, didn't cost too much. I'm struggling to remember the details but it is a common condition.