I serviced it today and gave it a check over, there's no split/loose boost pipes, there doesn't appear to be anything wrong with the intercooler bypass pipes, I tried unplugging the MAP sensor and that put the car in limp mode and was worse than before.

Hi Rob

Did you ever resolve this issue as I have exactly the same symptoms and was hoping for some clues as to the cause.

Cheers

Nelix

Still haven't cured the problem, I've tried a new MAF which has slightly improved things, before there was sometimes no power even after 2k, now there's almost always power after 2k but still nothing before. I've turned EGR off in the ECU, still no better, I may try physically blanking it off.

I have a new VNT ring to fit but haven't found the time yet, I don't think it's the bearings in the turbo, there's no excessive play and it still spins freely, although I did buy a brand new core just because it was a bargain price on ebay, it's going to stay in the box until I need it though!

Problem solved, the EGR valve was stuck open, that's why turning it off in the map didn't help, I fitted a blanking plate and suddenly it drove how it should! I thought I would have had a fault code if the valve was at fault but clearly not.

My MPG is slowly improving and it's so much nicer to drive, I've had stuck EGR valves before and they caused nowhere near this amount of power loss, maybe it's because it's only a 1.6 HDi, at least I sorted a few other problems on my way!

That's brilliant news! and thank you for sharing the outcome. Its always good to get an answer to why there was a problem.
More knowledge is always helpful!