misfire on 6k
 

i have a misfire on 6000 revs, went to mazda dealer and they suspect 2nd turbo is knackered(if so i wouldn't be surprised as when i bought it i had 2 intakes blitz-which was ok and HKS muschroom one but without filter in it - just a bracket, so it could have sucked some dirt in it)

but..

just wanted to ask as im still pretty noobie in fd's what else could it be? any similar common faults?

thank you