I have an 2009 focus (automatic trans) that rough idles specifically between about 1050 - 1450 rpms. When I start the car it usually is alright at 800 rpms but will occasionally jolt up to the rough idle.
I have replaced spark plugs, ignition coils, both motor mounts (haven’t done the trans mount), the valve cover gasket, and the entire electric throttle body. No clue where to begin repairing this. It doesn’t seem to be a vacuum leak and it happens while at a standstill and while at a constant speed while driving. I have not lost fuel efficiency (still get 29mpg while commuting).
Please help me.
Edit: no check engine light is on