My 51 plate p38 has a popping noise from air filter when rev'd up(not gassed up).It is lacking power and has a miss fire,we have replaced the following.New plugs,leads and crank sensor(been on diagnostics to be told crank sensor at fault),replaced down pipes(as some clowns cut the cats out).Had gas anylaser tube up its pipe and it has no issues with emmisions.Had the engine compression tested and all cylinders achieved over 175 psi easily.We have had the coil packs checked and they to are ok,very fustrating,any ideas boys(or girls)?