Boostjunky

HI Guys,
Ive got a scooby wrx sti type uk 03 plate, fitted with a cobra 3inch system and a k+n panel filter, which worked fine was really pleased. Anyway, bought a wrx hybrid blow off valve from scoobyclinic, fitted it on vented only and the scooby didn't like it, idled funny and made the exhaust louder. Phoned scoobyclinic they told me to fit it on the 50/50 setting, half to recirc half to vent, so I did but its still the same, when going on idle after driving it hesitates at 1200rpm then drops to 1000rpm then after about 5ish seconds goes to normal, it also pops out the exhaust now and then after full throttle on gearchange, the exhaust sounds louder, more raspy loud even on idle and its using about a third more fuel. Does it need adjusting or alternatively taking off. Quite suprised really as the guys down scoobyclinic said it would work a treat but then again, i've probably done something wrong just want to know if any of you guys have already come across this. Any info will be greatly appreciated.
cheers from ross