Just put new plugs in after 40'000 on old ones,had a misfire so bought NGK on flee bay called at garage 97 put in WOW better fuel mpg,at least the puter is saying also pick up and nicer sound on over run. Is it plugs or good fuel or both. after following links on forum pice of cake to do £38 for plugs on flee bay and satification of doing it yourself no ripoff from stealers. 
