Rough idle/start in cold weather?

[NJ04e53]

hi..i just picked up an 04 3.0i on monday and the following day it started to shake like crazy in the morning. It was like 30F here in NJ. The Service engine soon light came on. I took it to denville bmw and they said it was a misfire and took care of it. Light was off and i drove away. following day it started off smooth. Now, no light coming on but started to shake again. I stepped lightly on the gas and suddenly it quiet down. I will call bmw and let them know of this and probably stop by during lunch time since i work next to them. i really hope this is nothing serious..at least they told me before it was not. I guess i'm not the only one after all. I'll also look into all the suggestions that were mentioned in this thread and go from there. Thanks