16683 under boost help

[chris_rx8]

Engine is 2.0tdi BKD
i have the above fault which is showing car is under boosting, I did a log and you can see that the actual boost lags behind the expected boost as revs rise then drops into limp mode
I have also noticed like a hunting of the revs around 2k I can feel this driving under load and carefully reving up whilst stationary

I seem to have changed everything without success Any suggestions would be appreciated.

Turbo has been rebuilt and set up with correct (new) actuator movement and vaccum.
N75 valve has been exchanged off my other car.
Egr valve has been removed and cleaned
I also made a blanking plate with 5mm orifice to try.
I have changed mass flow meter off other car.
changed the egr valve/cooler for new on rear of engine
checked vaccum hoses with a vac pump

so my thoughts are is there a restriction in the boost side i.e. intercooler maybe I need to remove and clean/ check?
Perhaps the CAT is blocked?

Any one have suggestions to try as at a loss at moment

 

[max69vk]

Check the boost pipe connection especially at the intercooler, the clips are a crap design & prone to working loose & leaking boost.

 

[chris_rx8]

Yes good point, I had thought to see if I can change the seals to be sure.
but I think it's something else, wondering if its the throttle body that will be my next change.