1999 s40 sluggish

[cosworthwrc]

hi all, done a service on a 1.8 s40 which was running rough to start with.
since doing the service of which i renewed the plugs and fuel filter, it is still runnig rather sluggish. ive heard that they suffer with a lot of head gasket problems. any suggestions before i start stripping the head down???

[Slomo_uk]

have a look at the coil packs 1st.. Most probably that.