Re: low power on 147 mjet until turbo cuts in
as above, egr as you've done the maf, then.
disconnect the vac pipe that goes to the turbo actuator, do you have a good vacuum (may take a second or two to build up on the end of your finger)
If not, check for leaks and prove that the over boost module is working, then work back to the vacuum accumalater at the back of the engine, also check the vac pump on the n/s of the engine at the top.
If you do have vacuum, reconnect to the turbo, have someone else start the car and you should see the actuater pull in by about an inch.
If it doesn't, can you move it by hand or does it feel seized?
Don't force it to the point of breaking anything, as you may be able to save the turbo if thats the problem.
Sensor involved will be the MAP sensor on the intake manifold at the back of the engine. circa £35.
Also the VNT controller/overboost module on the front slam panel, you may prove this is faulty. circa £40
If it all points to the turbo, you can remove this and seperate the exhaust housing.
DO NOT try hand remove the turbines, these are balanced.
The exhaust housing is held on by the 8 or so bolts you see around the outside, remove these then you will be able to remove the exhaust housing (may need to use a release fluid and a bit of heat to penetrate to make removal easier)
Once removed, take pictures for reference as you go, you can then remove the VNT ring, then mechanism which is held in with 3 small torx bolts, at this point you will be able to inspect and clean everything up.
I have seen build up of corrosion/muck in the mechanism side which can cause the VNT to stick, you can often clean it up with a flat blade side of a stanley blade - you will be amazed at how much you scrape off.
This is no way a guide, and don't do it unless you are mechanically minded, but contrary to belief, you can take these things apart, inspect, clean them up and put back working.
Just DO NOT tamper with the main centre parts with the turbine wheels in, these need balancing and carefull setting up, the VNT side in the exhaust casting is a very simple method, but you do need to put it back correctly - its not difficult once you got your head round it.