Hi all

Just collected my RS after 7 weeks away and driving home it was running great loads of power, stopped off for fuel and all was well. Started off again and the car appeared to of lost 60% of its boost. Got the car home and noticed a funny smell so a quick look around and I noticed that the header tank had pressurised a lot. Released the cap slowly as the water would of spilt over. A look at the plugs and the oil cap don't show any signs of a head gasket and the car doesn't have any misfires.
Can anyone shed any light on this pls
Car is SAbre mapped to 330 and has uprated hoses, intake, exhaust etc along with an uprated Dv and wastegate.