You need to have a source of vacuum to operate the vane actuator to ensure it moves freely. I suggest you find an independant specialist to first collect some live data whilst you are driving as this may not be a turbo issue but a MAF problem. The indi with have all the gear to check the turbo. Regards Peter

I would start by checking the free operation of the turbo actuator.

How do I do this ? :)

Thanks

Find the diaphragm that opereates the turbo vanes, which should be apparent near to the turbo, remove the small vacuum hose and replace with a pice of hose you can suck on. When you such you should see the actuiator move and then return to its resting position if everything is working okay.