2011 C250cdi inconsistent boost

[cmal1001]

Hello all i hope someone could point me in the right direction. I recently took ownership of a 2011 W204 C250 cdi blueefficiency and i do love it! Great mpg's however there is something that bothers me. The boost is inconsistent in my view, sometimes you will floor it and the car will throw itself towards the horizon, and other times its like a gradual pick up...not much in the way of torque. I know the smaller turbo works as you can hear it spool up when you take off but like i said the 2nd bigger turbo i assume is to give you the real power when you hammer it sometimes its just not ALL there, there is power its just very inconsistent, floor it in 2nd gear at 2k revs and you sucked into the seat do it again and its like....ummmm are you going merc? or what? Is this is a common issue, is there something i should be doing or checking?

P.s its a manual tranny, ive just dumped some Hydra diesel blast into the fuel tank just to clean off the injectors as i heard they are notorious for gunking up.

Thanks