hi mate, iv,e got a gti and mine started doing the some thing about 4 mounth ago. 3000k plus rattle under the car. i had the mas air flow changed plus spayed the lot with wd40, but did not help in anyway. i disconnected the battery to reset the ecu and it seemed to do the trick the revs went back to normal. but when the car got hot it started to lose power until i put the accelorater to the floor and then it would put ya back in ya seat. the car is in at FORD at the moment for the 6th time for the same thing. i dont no if they no what they are doing?. hopefully yours is something simple. the cars due back any day now so i'll get back in touch with ya and let ya know what the problem was, thats if they fix it.

Toniboy