I am not sure why you are bringing the temp up to 400 and then shutting down the intakes. It is very hard to bring temps down so bring the temp up slowly and not over fire the UDS. I am a bit anal so I use a DigiQ and never have to worry about temps. I light a few lumps in the chimney and dump them on the basket full of lump and put on the lid. When temps stabalize, about 1/2 hour I put on the meat and that's it until they are done.