Most VW/Audi things if problem with immobiliser it will start and stop after a few secs.

Needs fault codes reading , no good guessing..

Usually shows up 17978/P1570/005488 if 'engine start blocked by immobiliser'.

http://wiki.ross-tech.com/wiki/index...8/P1570/005488

If key and or reader coil faulty possibly this code

http://wiki.ross-tech.com/wiki/index.php/01176