Aaron started it but IMHO was not able to finish it to my satisfaction. Did a bit of the fine tuning myself re idle and boost etc, and let Sean do the actual AFR side. Car is very driveable on the street and puts out good linear power at the track. Also tune is conservative enough in my opinion to survive the rigours of track work. I guess time will tell.
The PID is Proportional, Integral and Derivative gain. Is used for the boost control, idle control etc. Is some complex algorithym stuff. I am sure there are some propellor heads who can explain it. Is basically a way of getting the motec to perform in particular ways to ensure the set targets are hit. I have a useful PDF doc on it. Also try google. Heaps of info out there on it. Is a bit of a brain buster (well is for my commodore 64 brain) to get your head around but well woth the effort if you are into tweking your own tune.