OK, so I did my burn-in for 2 hrs. and then used a pellet tube for an hour to put smoke into it.
Then the autotune. Knowing that I could redo it if necessary I chose to do it with an empty smoker. I set the program to 225 for 3 hours, and started the autotune. When it was done (less than 2 hours), it maintained 225* steadily for an hour, so that seemed good. My numbers, OTOH, seemed at variance with other numbers I've seen. My numbers were:
P 57
I 259
d 67
Do these numbers make sense? Am I ready to start smoking (first project will be smoked jerky) or should I redo the autotune with a load?
The P value seems a bit slow (lower number is faster than higher number).
I'll explain it using your numbers.
When P hits within 57 degrees of your set temp it will begin to power down the heating element from 100% out put.
So when Set temp at 257 and the smoker hits temp 201 then the PID will ramp element power down to like 98% total heat/power output.
The "I" and "D" values will try to kick in but also often take their ques from "P" making "P" the lead value to play with first.
When Smoker temp hits 230F the PID will have power output to 48%.
So with these numbers, every degree increase is about 1.8% decrease in the element power.
So when the smoker is at 256F degrees the PID will have element power/heat output at 1.8%
That may sound confusing but in short the closer you get to your set temp the greater the decrease in power output to the heating element.
So the higher your "P" value the earlier the ramp down of power to the heating element becomes.
A higher "P" value means longer time to ramp up and hit your set temp.
A lower "P" value like a 5 means that the at smoker set to 250F degrees will be 100% power output to a smoker temp of 245F then at 246F it will ramp down to 80% output (20% per degree in this case).
This can lead to some overshoot of the 250F set temp when the smoker is initially coming up to speed or after opening the door BUT that overshoot only happens in that case when the "I" and "D" values are turned well and your I-D values seem to be in the ballpark so I think they are ok.
In conclusion, if it takes a little bit of time to initially heat up or heat up after opening the door than simply decrease the "P" value to something like 10, 7, 5, 3, or some sensible value knowing how it behaves when you observe it as you use it.
I threw a lot of info at you here so be sure to ask any questions you have :)