I support the recirculating BOV valve diagnosis. The stock BOV is more of a ABV. ie an Air Bypass Valve. When at vacumn, ie not on boost, the valve is open and allows air to go "forwards" by bypassing the turbo/supercharger into the throttle body. When at boost, the BOV closes up, allowing boost to be built, then when you let off the gas, the vacumn takes back over, the valve opens up again and the excess pressure (boost) bleeds back off to before the supercharger/turbocharger, basically equalizing the pressure of the system.
I had the same problem when I installed a BOV from a Supra onto my Supercharger setup and the car wouldnt idle worth a darn. Then I realized what exactly the ABV on the supra part really meant. I ducted it back into the intake and havent had a problem since. I would love a real "pshhhhh" BOV but dont really need one becuase of the relatively low boost I am running.