Cooked my first butt last night and had trouble keeping the dome temp where I wanted it. I thought I had the fire stabilized for about 15 minutes at about 250. I had the plate setter legs up. Don't remember if I put that in before or after getting to temp. I put a foil drip pan under the butt - did not put anything in the pan - it was dry. After cooking for about an hour I checked and the dome temp was up to about 375. I poured a large glass of water into the drip pan.
I kept closing down the chimney and the vents on the bottom every hour. Could never get the temp down to the 250 range I wanted. It cooked most of the time at an average of 340 I'd guess. Near the end I had it down to maybe 300. The bottom vent had the screen closed and about a 1/3 opening for air. The top chimney was almost completely closed. I was afraid if I closed them anymore I'd shut it down.
Maybe it had something to do with the way I built the fire? I read a few posts about how to layer up - big lumps on the bottom, medium lumps on top, the smaller ones up to the top. In my half-used bag of Big Green Egg brand charcoal I'd say it was 95% medium and small lumps.
I've got a Maverick ET732 but only the food probe works. I fried the grill probe like an idiot, so I need a replacement. Maybe I could have managed this better with closer supervision of the grill temp.
Anyway, any thoughts on how to get a true low and slow next time?