Nice bumping of an old post, but anyway...
I think you read it wrong mate, he doesn't have a plumb back anymore.
Basically (if that's even possible), the air goes past the Air Flow Meter, and whatever that reads, the engine thinks is going into the engine, so it puts the fuel in to keep the air fuel ratios right. It goes past the air flow meter and THEN it goes out the bov... so no air in the engine, but plenty of fuel... it can make for a rough idle and it can also stall after clutching out.
You can simply move the AFM to the intercooler piping, nearer to the plenum the better, to fix it...