It's not the MAF: ECU sees enough flow of air volume
It's not the Intake, This will not trigger low boost pressure in fact the opposite! Clogged intakes result in sufficent boost being generated however the restriction throttles the motor lowering Mass Air Flow hence reducing injected fuel quanity and then results in lower injected fuel. The end result is NORMAL boost pressure BUT LOWER TOTAL POWER OUTPUT! Typical of this condition is that No codes are triggered! Why? Simple, you are achieving specified boost pressure, You are getting the proper ratio of air volume for the amount of fuel injected and the engine is not at risk of producing an increase in emissions! As long as that pressure to volume ratio stays within normal ranges you will simply suffer from low power output and no associated engine codes!
BUT you do have a code so we know now that it is not a plugged intake!
The MAF sees the air volume, so the MAF is working properly. The MAP sensor is reading pressure and temperature correctly so its not the sensor. The engine is injecting the fuel but for whatever reason it is still not getting the bang for the buck so to speak from the air and fuel it is telling the engine to inject!
Therefore:
It is possible you have a leak in the intake system that is venting the compressed air out of the induction system. A very close inspection is warranted and this code is what will be triggered if you have a pipe or connection that is loose or not connected.
However you can't stop there!
A leaking N75 may cause the vacuum to be dumping and not driving the VNT to the full boost position. The N75 may be getting the signal to pull the VNT vanes to a full boost position however if you have abused the motor by NOT pushing this motor to normal load ranges (lugging and short shifting as if it was a 1900 rpm Redline) then you may have have a VNT that cannot move thru its required range of motion and is jammed in a low boost position hence preventing correct HIGH boost from being achieved.
If you lug your motor around and short shift at 1500 or 2000 rpm then you may have trashed your VNT system and have jammed up vanes. Carbon will form on the VNT system and prevent the guide vanes from moving accross their full range of motion. This will stop the turbo from making rated boost pressure. The VNT is commaned to full boost at idle to permit the fastest response from the turbo. As you accelerate and the ECU sees the boost pressure rise (500 samples per second) the ECU commands the N75 to decrease the duty cycle of the VNT actuator and thus reduces the guid vane position to a lower boost setting. In your case the VNT actuator is full open and the engine is still not seeing the ECU's expected/anticipated/calculated boost pressure!
If you drive the car properly (Shift at 3000 rpm, floor it on a regular basis and understand what Load is) then it may be the last item below.
The last thing it could be is a jammed or jamming fuel shut-off selenoid. This restricts the flow of fuel to the plunger and prevents full boost pressure due to low gas energy. This is a last resort if you have verified:
-Full range of motion of the VNT
-Verified good N75 condition in respect to sealing
-Good/new vacuum hoses in the system
-Verified good sealing of all the hoses and ducts on the pressure side of the turbo.
-Have no leaks in the intercooler from rocks
-No other component codes that can generate incorrect ECU base data for determining "Specified" boost pressure.