HI everyone im new to this forum and from any forum that is my first post ever (im french leaving in uk sorry for any fault in my post)

SORRY TO WRIGHT A BOOK BUT I TRY TO BE VERY ACCURATE DESCRIPTION OF SYMPTOM THE CAR HAVE

last september (2013) i brought a audi a6 2.0 tdi sline 2007 multitronic with 80000miles with full dealer service story with 1 year warranty from warranty direct.
from there the car was a nice drive smooth and nice no fault in October i drive to Paris for 2 week holiday with no problem at all .
2 week after back to London i was driving to the shopping center at 25mph the pulley from cam belt seize call AA and bring the call to the nearest independent Audi garage the diagnostic was cylinder head was smash need a new one for 2500£ with labor (Warranty paid 70% of the claim).
im back to the road 2 week after everything smooth again .
in December 2013 the the car start to judder badly when changing gear i call up my warranty they book the car for diagnostic the next day .
The day after have got a call from my warranty they send the car to A1 premier transmission my gear box need a rebuild
A1 premiere transmission couldnt rebuild the gearbox was to bad so they get a second hand gearbox with 40000miles. set me at 3k warranty direct payed
70% of the claim i fork out the rest .
again back on the road after 2weeks .
OK lets keep going still out of luck in february 2014 have got a new problem the car start smok form exhaust (light grey) when stoping at light but when on motoway cruising is nothing he hapen only when stoping at light or when parked (NO Warning LIGHT ON DASH) So i book it to the mechanic after checking dpf,egr,turbo,and hose and tell me the proble coming from 2 injector i need new injector seal kit i paid 475£ for all job oil change and new filter.
when i went to pick up the car me and the mechanic went for a run car is still smoking but less than befor he tel me is because they pute something in the diesel the clean carbon build up . i said fine and took the car away ( by the way don't bring ur car to prestige car in forest gate unprofessional staff and rude )
the car his still smoking and still have the same symptom till last week ,now turbo over-boosting idle stay at 2Xrpm when foot off the gas for about 1mn (no sure if is overboosting or something else) and when is come back to normal idle he give alot of grey smoke 5 day ago i try to pullout from my house have got bad judder from 1xrpm to 2xrpm so i revers and leave it on my drive way.
Today i open the engine bay check for any leak from pipe ,actuator ,ect but couldnt see nothin from the top of engine couldnt chech the intercooler
(but the car is no loosing coolant) and i couldnt see any oil leak on the bottom of the car (didnt check under engine tray)
i started the car and still light grey smoke, and now have got the fan running from star of engine is it normal ??
i rev it a bit i hear the turbo slightly hissing and when i took my foot off i have a strange noise like dump valve ( relieve pressure) or something like that
maybe a leak ? ?

i know alot about car i owe audi a3 1.8t (00) bwm 525I (02) ,range rover hse 4.6 (99),ford mondeo 2.0tdci (05) and now the a6 give me alot problem im very disapointed with Audi .

so could someone with more knowledge than me and good in audi mechanic point me to the right direction please .

(i cant sale the car is on finance still got 5k to pay or wait next year for part ex)
i realy like this car is a good cruiser.


( turbo as been replace 2 year befor i own the car)