Problems with mercedes (c-240)

Ok guys I want to fix this problem myself or at least diagnose it, I recently purchased a 2005
Mercedes c240 from someone they said it had a little smoke coming out of the tail pipe every
now and then, when I arrived at the destination almost 300 miles from home I purchased the car
not knowing it was a serious problem, at first it didnt smoke, well very little when I started the
engine but as I got on to the highway, the car blew this massive amount of smoke out of the
exhaust...like so big it would blind the people behind the car for a min as well as it would sputter
and have a loss of engine power. Also it was losing massive amounts of engine oil, at first not
bad... it came on like 100 miles down the road and told me to add a quart then more frequantly
as the trip went on I believe I added a total of 4 quarts throughout the 300 mile endevor. And
probably spit out 6 to 10 big clouds of smoke... since its happened I have read all these blogs
about different colored smokes exiting the exhaust pipe however I dont know how to classify
the color it seemed like a light blue or white... and of course the check engine light was on from
the start. The guy that sold me the car assured me that it was a pvc valve or something like a
150 dollar part to fix... in any case, I kept adding the oil as the cars computer told me to do and
babbied it till I arrived, I plugged my OBD tester in and it gave me a reading for a misfire and  a
couple other things I cant remember, I realize now that it is a serious problem but I am  
construction man not a Machanic... however being that I dumped all my extra cash into this
thing I am hoping maybe I can get the right advice and knowledge to fix these issues.  Im
assuming I need to check the 3rd cylinder over for the code said something like p303 or
something like that... anyway any advice/help would be greatly appreciated. Thanks for reading
and hope to hear some promissing news