07wrx gt30 etc.. AFR lean at idle...stoich at wot

[Obababoy]

So my car had some adjustments done to the tune to smooth it out under vacuum.

I have an 07wrx with a perrin gt30r, hks ssqv2 bov, and a utec delta etc etc...The car was running great after his retune no CEL, good AFR's at startup and idle...right around 14.5 under normal driving and idle.

Well I had a good hard run the other night at a track with it running around 150mph for maybe 10sec on a straight. Everything good! I let off the gas a couple times. Heard the bov working well...let car cool down turned it off for the night...

Next day I started it up, drove about 10miles and realized my AFR under veeerry easy throttle and idle was like 16.5-18...I got on it and AFR was fine, car made the low 14psi as normal(but seemed a tiny bit louder, almost like an EWG dump but much quieter).

Questions:
Could my BOV possibly be worn out causing it to leak at idle and very light driving? Tuner put it on used.
Idle is searching up to 1800rpm with clutch pushed in until I come to a stop then it settles to normal?
Is this just another anomaly with me using a UTEC and Big MAF?
What could cause RPM's to hang when I let off after WOT?
Could it possibly be louder by removing the plastic undertray from engine bay?


Any Tips or Suggestions would be greatly appreciated.

~Chris