I've noticed now that when I sit idling the car will sometimes rev a little higher then drop to normal. I'm talking about a maybe 50 to 150 rpms more but definitely noticeable. Kind of like stumbling/shaking . The plugs have about 40K on them, filters are new and I change the oil every 3500 and substitute 1 quart with Lucas oil. Car has 123K it's a 2014 EX.