Originally Posted by Ron_L
Make small changes and then let it settle before changing again. Otherwise you'll end up chasing the temperature as you said.
What Ron said.
A new cooker may not seal as well and be a bit difficult to control as a result. As smoke builds up on he inside and as you get more skillful with adjustments it will become easier.
And in the mean time rest assured that temperature is not critical for getting top notch results. It may matter more for hitting a specific target time, but when your food is done it will still be good regardless if you went a little higher or lower than you wanted.
Of course we should be saying "pictures or it didn't happen!"
Edit: I agree with everything rwalters said too, I just didn't see his comments before I posted mine. I do use water in the pan except when I want higher heat for stuff like chicken or turkey. It helps prevent overshoot so I recommend doing so as well. It's like training wheels. You can take them off when you no longer need them.