I am having a similiar issue with my 147 JTD and would be interested in whether or not you have managed to fix your problem and how.
If any one has any idea on how to help with this I would really appreciate it, its been an absolute pain in the backside for the last month or so.
A bit of background on mine;
When I start up after not having driven for a day there is no ECU light. Heavy acceleration in low gears doesn't seem to affect the ECU however there is a high pitched squealing noise. Once I get into the higher gears heavy acceleration or maintaining medium acceleration on flat or incline results in ECU light coming on and all power being lost above 3000rpm (cannot barely get over 3000rpm). To give a perspective of how low the power is, I start losing speed with my foot down on a slight incline on the motorway doing 70mph!
So, if I stop and restart the engine immediately the ECU light comes on but acceleration is back to how it was before until I accelerate as before in high gears. This time there is no noise from the car, (the ECU light is already on when i restarted) and with no warning the power is gone.
I've had my EGR valve, MAP sensor and a turbo pipe changed to no avail
I took it into a diesel "specialist" who said my vanes were stuck on my turbo as the ECU was coming up with overboost. This theory was soon eliminated by carrying out a simple check on the turbo vane actuator whilst getting someone else to start the engine. Actuator moved fully if a bit slowly. I unplugged the vacuum hose and took it for a drive - no boost until about 2700rpm and then I get normal boost. This suggests to me that the vanes are definitely moving as I get boost at low revs with the vac hose on and at high revs with it off. Infact when I plugged the vac hose back in the actuator was moving much more smoothly than before!
So I thought I'd narrowed it down to the VNT Solenoid which controls the vacuum to the actuator and hence movement of the turbo vanes. Swapped this for a new part but the car is still running exactly as it did before.
Do I need to clear the fault code for it to make a difference?
I'm running out of ideas now, can the MAF be giving lower readings than the actual resulting in more air in the engine than the ECU thinks? but then this wouldn't be overboost. Piping seems to be fine too, couldn't be the vac pump could it? Or could it be an incorrect MAP sensore fitted? there is a difference between the 8v and 16v sensor right?
Any help would be more than welcome, I am at my wits end with this and do not trust any garages to have a look at it now! The garage that told me the vanes were stuck recommended I replace my whole turbo with a new one and quoted £800 for just the part!!!!!!