hi all i brought my moonstone 2wd sapphire cosworth about 3 months ago, almost immediatly after purchase it developed a fault that to date seems incurable!

when idling the car occasionally hunts between 600rpm and 1200rpm ocassionally cutting out when driving when applying the clutch to stop at a junction etc.. also and more concerningly when you apply full throttle when it hits boost it hesitates and misfires its head off! half throttle seems ok, it has +.50 mahle pistions, standard cams, ported head, bosh 803 injectors, stage 3 chip, ar63 turbo rs500 intercooler, 3" exhaust system. grp a coil, wrc head gasket and arp stud and nut kit
to date i have had the head refurbished, replaced plugs, new cambelt, tensioner and cometic wrc metal head gasket fitted new grp a coil but thus far problem still present!
please guys if you can spare some time to throw some suggestions at me as im running out of ideas (and money lol!)
cheers stu