Audi A6 2.7T

[Niti]

I have an Audi A6 2.7 Biturbo.....Im having a problem with it....it shows the check engine light and sometimes it shakes, had to mechanic said it could be O2 sensor....and also when i push the car hard the turbo goes on but when i let go it kicks back dont know why ?....If anyone can help i would appreciate it.....or some good and cheap mechanic in Mississauga or Toronto.

[Omnipotent]

post in the A6 section...