I will suggest that you should figure it out what's wrong first before moving forward with tuning. Did you check the line that connects the PCV valve? Sometimes they tend to leak.
Well, with that many miles and not knowing the history, I would suggest that you should do a little deeper on the maintenance to check the health of you engine just in case. You mentioned that it idles very well and it doesn't have any DTC's, but does it drives well around when is not under boost?
Like one of the guys suggested, increase the pressure to at least ~25-30 psi to hear any noticeable leak if any.
Have you done any maintenance since you got it?
Those are the things that you have to deal with the standalone route. I believe the microsquirt will ran out of I/O pretty quick. But now there's more options out there as far for ecu's. The other thing is the CAN Bus integration if you want to keep everything working. There's guys out there...
Not yet. I was doing some research for BT setups and I came across this topic.
I have a new BT setup (6062) with PI on my genwon that I'm trying to dial in.