Fluttering is kind of confusing. Are you "lugging" the engine? Try downshifting without increasing your speed. That will raise the engine revs. The programming of some of these cars is designed to upshift early in an attempt to increase fuel mileage by decreasing revs, but at times that can cause lugging, which eventually leads to nasty things like carbon buildup or ring failure. See if a lower gear smooths things out.I have a 2014 cadillac ats 3.6L awd. While going uphill at about 10-20 mph it feels like the engine is fluttering, if I get on it, it goes away. There is no check engine light, no codes to read! What could the problem be? Check engine light is not flashing, so I kinda ruled out a misfire.