Low boost P0234 P0299 problems

[andythepandy]

Hi all been trying to troubleshoot a problem on my wifes car but I am having trouble tracking down the culprit

Car info:
2007 XC90 D5 Euro4
135,000 miles

The issue started a few weeks back with a 'Engine system service required' message on the DIM. It also manifested itself in the car having no boost when under heavy load. My wife has also reported that when it loses power she can hear a woosh noise. I also from memory remember that the car has been making a mild whistle noise on boost for several weeks.

After plugging in my cheapo OBDII sensor the codes that came back were: P0234, P0299, P0601 which I imagine are all related

Also might be related but the Turbo actuator was repaired shortly before purchasing the car in January

I have pulled a few bits off the car this afternoon to check the usual suspects:
All the vacuum lines look in good condition and not perished,
cant see any splits in boost pipes anywhere,
the boost control vale looks ok (might replace this anyway just incase),
the resonator pipe looks secure and not split or loose (again might replace as I know these fail regually),
one of the wires to the Maf was just about hanging on but broke when I moved it (I don't think this was an issue as it threw a MAF fault code up after I broke this)
Other than that where should I be looking?
I can't quite see the intake to the turbo as its obscured but I'll try and get in there

Has anyone got any other ideas as to what I can check?