[Carfixer2]

The vacuum operated bypass valve is different than the wastegate actuator. As Mimmi states just do a test with the hose disconnected. The wastegate is opened by the pressure produced by the turbo. The boost pressure control valve bleeds off some of that pressure to get you from base boost (about 6 psi) to full boost (between 9psi and 15psi depending on factory settings). By removing the hose the wastegate will remain closed and boost to unsafe levels. If you would drive this way you will be putting in pistons or valves when they burn.
Remember your boost gauge in the car is not reading the psi of boost. It is based off how much air is going through the MAF. If the MAF is failing it often reads low. So it is not putting in enough fuel. So if you undo the wastegate you can burn up the valves or pistons even quicker if you try to drive it that way.
If you have full boost with the hose disconnected you might need a boost pressure control valve. If you still have low boost you might need a turbo.

 

[Carfixer2]

Even though T7 has a Map sensor it is not used for the Turbo gauge in MIU. It is used mostly for self diagnostics. If you look in WIS under MIU and go to the description for the Turbo gauge you will see if uses the MAF for the reading.

 

[Carfixer2]

I believe many engineers subscribe to the motto : Why do things the obvious (simple) way when you can make it complicated!

 

[Carfixer2]

Is the wastegate actuator still attached to the wastegate. That P1105 almost sounds like the code you get when the clip holding the actuator onto the actual wastegate lever falls/rots off allowing the wastegate to get stuck in a fully open position.

 

[Carfixer2]

Correct it pushes it with pressure.

 

[Carfixer2]

Yes, just to give you room to work. It's the aluminum tube running from the bypass/recirculation valve to the turbo inlet pipe. There is a o-ring on the inlet pipe side.

 

[Carfixer2]

If you are pressurizing were the MAF sits you will need to remove the banjo bolt there that goes to the pcv. It is before the turbo so there is no check valve or anything in that line. The small hose on the pcv nipple on the valve cover is the only connection to the pressurized side of the turbo. It should have a check valve in that line between the nipple and the throttle body were it attaches.

 

[Carfixer2]

In the tube from the MAF and the turbo there is a banjo bolt attaching a metal tube to the aluminum tube. That pipe attached to the banjo bolt attaches to the pcv/oil trap/oil seperator box.