Hey guys, I own a 2019 mustang GT 10-speed automatic. This past Monday, I experienced a rough idle & a change in rpms when I was at the red light. Never done that before. I thought nothing of it but it kept doing it again. I changed the spark plugs, I took it a quick lane by the ford dealership & they didn’t find anything wrong with it. They checked for codes. Only thing that popped up was “unexpected RPM change on crank”. I only have a resonator delete & cat back delete. Nothing else is done to the vehicle. Any ideas of would could be wrong with it? Could it be a vacuum leak? Exhaust leak causing the issue? I’m not sure. Next thing was to replace the ignition coils. Anything helps! Thanks guy!