New EGR valve - same fault code

[such01]

I had a couple of fault codes 14B700, 14B800 after going into limp mode (no warning lights) suggesting an EGR valve stuck closed/open.
I have changed with an aftermarket brand Lucas, but the same problem arises shortly after driving.
My original egr valve did not look as bad as I thought considering the 190k on it.



Before swapping out, the car would be fine for a few months after restarting (maybe I should have just left it), but now unfortunately not so.
Not had any other issues prior to this - car was driving fine.

I also changed the exhaust back pressure sensor due to brittle plastic around the plug breaking off. MB part.
Any suggestions? Alex Crow cannot look at this for at least another week.

Thanks

 

[such01]

MB tech came out today and diagnostics read
"air mass values out of range at 20-40% open. mass air flow sensors passed test"
He suggested a smoke test on the air intake to check for leaks and to check the EGR cooling system for potential coolant leak

I have driven the car since and it is defo down on power and changing gears before 1.5k rev with no real acceleration.