hello kessa and welcxome to the site!!!
ive got a mk4 gti 20v non turbo, ive had some probs (cambelt tensioner failure=engine smash up!!!) and had to rebuild but since then ive been havin a few teething probs!!!
will try to help you with your prob if i can.... 1st off what model mk4 gti do you have???
engine size/type would be a great help in starting to try and diagnose your problem??
Gaz