Boost pressure sensor is high, putting it into limp mode.

I guess the turbo could be on its way out, but I guess I should check:

All intakes clear and clean.
No vacuum leaks.
Clean the EGR (may as well insert blanking plate with hole while I am there).
Clean all MAF sensors that the EGR has gunked up.

Anything else obvious I should look over?

Check VTG actuator and VTG vanes in turbo. High boost pressure warning is typical of a VTG actuator problem. The vanes are set to closed (max. boost)at idle, the vacuum driven actuator gradually opens them up as exhaust pressure increases. The mechanism has a tendency to bind over time, especially if the car is not driven regularly, is used in city traffic only and/or puts out more soot than usual due to gunked up intake, malfunctioning EGR or a leaking intercooler.