bought a MK 4 GTI on saturday, im feeling somewhat done over though, car seems to drive fine when first started but after about an hour or so the exhaust starts blowing as if it were something to do with the coilpacks or plugs..only problem is, i had it plugged in and the fault its showing is turbo boosting too high...any ideas on this one? the car refuses to go past a certain amount of revs unless i downshift when its playing up and then boot the backside out of it...doesnt mind sitting at about 3grand on the revs though. car has cut out when idling and also whilst going round a roundabout in 2nd gear...also on the motorway at about 70...bit worrying...any help massively appreciated!