2005 Mercedes-Benz C240 Question: check engine light on, sputtering on start up and white smoke

The check engine light came on. Not really sure when, could have been after driving it up to 120 m/hr for a few minutes. It has been having problems starting in the mornings since it has been cold over night. It sputters on start up and sometimes needs two tries to start. When we stop at a traffic light the rpm go down so low that the car seems to want to shut off. This morning the car did not start at all. When I turn the key it sounds like it wants to start but can't get enough gas (this is just my female non mechanic input!!)after 15 seconds or so of trying to start running it shuts off. After it finally started, after about 30 minutes of trying and letting it sit for 10 minutes, a tremendous amount of white smoke was blowing out of the tailpipe. I did not want to get stuck on the road so left it at home. Any idea what this could be?