I recently bought a kc combo grill and am using the smoker for the first time. The temperature is set to 250 but goes as high as 350 which is ruining my cook. I read that a 50 deg difference is normal. I have the flame broiler closed. It seems that when fan is on the temp jumps significantly. The cap is all the way open. Not sure if im doing somerhing wrong. Im am cooking a pork shoulder. Any help is greatly appreciated since this is my first cook.