As per Steve & Matt, the breather valve causes issues on these,on the Golf they have also sludged up & stuck, the 1.8T is a sludge manufacturing unit - VAG USA are being screwed in the USA for massive No's of engine failures due to the build up of sludge. Also seen one with a split suction jet pump & another with the rubber 90 degree elbow split on the underside of the manifold, between intake for cyl's 2 & 3 - which only let the smoke out when smoke testing if you pushed on it.
We pull the manifolds off these & change the vac pipes /hoses /breather valve & suction jet pump.

How does it accelerate when booted up the road? The 1.8 turbo engines tend to break dance up the road on acceleration, (in the same way as a points ignition engine would with a failing condenser) when the MAF is failing.
And finally - is the turbo spooling up? the oil supply lines block, (with the aforementioned sludge) & seize. Make sure the turbo is building up pressure. The "dump valve" diaphragm spits as well causing an internal air leak, but this usually logs a pressure drop DTC.

Jon