The first time I cooked on my WSM, I got the temp up to 230 at the top grate (probe run through a 1/2 potato) & 250 in the dome (candy therm in exhaust vent). It stayed there perfectly for the longest time without me having to do anything.
I began to worry that something was wrong. It just didn't seem right that the WSM would hold such a consistent temp for so long without me having to do anything.
After about 2 hours, and way too may trips out to the smoker to see what the temps were, I convinced myself that it was going to start dropping soon, and I needed to do something.
Rookie mistake: I lit a chimney of coals, and when ready put about 8 to 10 of them in the WSM. This shot the temp up to 275. I then fought with getting the temp back down and getting it to stabilize again.
Lesson learned: If it ain't broke, don't fix it !!!