2015 ATS 3.6 RWD Premium
The smoke upon startup is one of the indications of valve guide seals requiring replacement. Hopefully the stealership looked into that for you. Also, take a look at this thread: http://www.cadillacforums.com/forum...-also-experiencing-rough-idle-my-brand-4.html. Consistent problem with the 3.6 DI engine.