Mondeo mk3 help

[gtm88]

I have been reading alot on this website these last couple of weeks and it seems many are having or have had the same issue as me. Mk3 2.0 tdci mondeo, 70k on the clock 55 reg. A few weeks a go I was driving on an a road, went to put my foot down and the coil light flashed and it went into limp mode. Typical ignition off and on and it was fine. Did it again maybe 3 days later. Put a can of bg44k in to see if that helped at all and it seemed to be fine for maybe a week even when I tried to get it to do it again. Same thing happend again so got the codes read which were po251. Cleared the code filled up with bp ultimate and it was a different car, boosted better and for longer and the performance and fuel economy went up and up. Thought I'd try normal bp fuel and it was fine for a day or two. Last night is did it again so I once again cleared the code. Drove it to work and it was ok,  felt sluggish but no coil light. Cleaner the egr valve out to see if that helped. Drove the car home and it didn't feel as good as when it had the bp ultimate fuel in but it did feel more responsive low down. Turbo seemed to make more of a whooshing noise then normal, got 10 seconds from home and gave it a squirt and the !Removed! light came back on. My confusion stems from the fact it doesn't have many common symptoms of the usual faults. It starts fine never an issue, no smoke at all and the idle is never erratic. Looking around on the Web and asking various people and the usual suspects are fuel filter, egr valve,  split pipes, injectors or fuel pump. The only code it has supplied is the po251 and the fact I don't get the symptoms of most the usual causes is baffling me to be honest. Can anyone shed any light? the fuel filter was changed not overly long a go but I do think it was a euro car parts jobby so have ordered a Bosch one. Any help or suggestions will me very much appreciated. Thanks.

[gtm88]

On a quick note thought it could be a sticky actuator on the turbo but that seems to move freely.

Inlet manifold looked pretty carbon rich too but didn't have time to clean it out.

It's a 130 model.