S4 coil packs/ misfire.

[g338iry]

Hi , just bought a 03 plate( has 72k on clock) , covered 300 miles and now not firing on all pots !! Maybe I shouldnt have cleaned engine with Gunk and gently power washed it off !! I have cleaned out all coil packs ( all dry) , sprayed WD40 all over, ( the mis-fire didnt happen straight away after cleaning engine , about 25 miles later ) , my main question is about the coil packs which I have heard are a bit 'iffy' ???
Any comments would be appreciated .

Mark...