I don't, not even for a second, think that it's a gauge issue. I was just saying it's something to be aware of.
Bear in mind that when the actuator pipe is disconnected, the boost is uncontrolled, meaning that the turbo is working ok, it's something electronic stopping the boost from appearing.
N75 is a possibility, but to be fair, I'd say unlikely. They are pretty simple thing, basically a glorified on/off switch and rarely fail. When they do fail, they normally throw a fault code to suit. Firstly, is the N75 the right way round? A photo will help confirm this.
Secondly, AGU engines are very very highly reliant on the MAF. They have no MAP sensor to tell the engine management what the actual boost level is in the manifold, and therefore it has to be worked out via an airflow vs throttle body angle calculation. Thus the MAF does play a big element in boost control on the AGU engine (I speak from experience).
Here is what I would do.
If you have VAG COM and can log, you should be able to log block 118. It won't show actual turbo pressure, but it should still show N75 duty cycle, and this will tell you whether the thing is working or not, and if so, how much.
Secondly, I would try and find another MAF just to use for testing. Second hand, borrow, beg, whatever. Anything to use a MAF which is known to be working to save you potentially buying one when you don't need one.
Start by logging N75 duty cycle (if you can on the AGU). If you need to start replacing parts (on the proviso that the N75 is OK), start with the MAF - it's the most likely culprit.
