D4 2010 restricted power mode - low boost pressure

Hello all

I’ve had an intermittent fault with our d4 for about a year now. Comes randomly maybe once a week and puts the car into restricted performance mode.

I’m getting the code 1247 turbocharger boost pressure Low

I have read online and the most common thing is the manifolds cracking so I have taken it to be smoke pressure tested and could not find a leak.

I have removed the MAP sensor which was a little bit dirty and cleaned it out and still no difference

I’m not smelling any fumes in cab and the fault seems to appear any time when cold or warm but usually when driving steady. Happens a lot more now as I’m in Wales and every road is now restricted to a 20mph

Thanks in advance