This is my take on all of this:
I have had my car with open at idle BOV (my kit is routed like JDL's) and didn't pay much attention to it. It had an 8psi spring.
I've had a hard time tuning the idle for the past month. Looked for fuel leaks, vacuum hoses popping off, etc. Nothing was wrong. Yesterday I decided to try closing BOV and it is a different car.
Car is way more responsive, it's building boost sooner and more importantly, the idle improve significantly. Now Just need to fine tune for it and it will be within 2% of fueling error. I used the Tial chart and selected the 11 psi spring which is the correct one for my car that vacuums -20.
On the tune side, I used to have an FA20club tune that had these issues:
Idle dip... bad (never fixed)
14 AFR part throttle all the way to 16 psi (WOT would force open loop and proper AFR) (never fixed)
Too rich AFR when going to open loop, creating a misfire CEL when going WOT sometimes (fixed after multiple times asking for it and fixed only because instead of asking about the CEL and being told it was a bad coilpack, I actually diagnosed the issue myself and simply asked for an open loop AFR leaner than high 9's
Car would not start normally, needed to start cranking then WOT to remove fuel and make it start. (Fixed after spending money on FA20club recommended injectors sworn to have those ones nailed down perfectly, still having the issue for a couple more tune revisions SMDH... but then fixed for good).
And the weirdest of them all, sometimes completely random the car would make no power even at 16 psi. It was like ALL timing was removed from the tune. A little time later or stopping starting the car later would fix it. Other times it would not make power up to 10 psi and then would make normal power from 10-16 psi.... Never ever got this resolved and know other people with FA20club tune that have hd this happen too.
Heck, less than a week ago I reviewed logs from one FA20club turbo car dyno tuned with FA20C turbo and one dyno tuned by FA20C but with P&L turbo and both of them knocked while cruising to -5......
All of this issues are non existent with @
jamesm tune.