I have a 2006 GP GT with 174000 miles on it. About every 1.5 to 2 seconds or so, at idle, I notice my engine go from about 700 rpm to about 600 (rough guess). Then it goes right back up. When I'm standing behind the car, I can hear it either puff or poof at the same interval as stated above. I'm not sure if that's a misfire, because most of the videos i've seen regarding the exhaust putt putt, occur at a much faster rate than mine.
My CEL isn't flashing, and I don't notice anything wrong when I'm driving, the only time I notice is when the engine is idling. I'm going to check my plugs again, but could use some direction.