A friend of mine has just bought a S2 90` Spec turbo, it has devoloped a misfire since shes owned it. However, if you pull the lead off No.4 plug and rest the lead close to the plug then it runs fine. Just when you connect it properly, it starts misfiring.

We`ve changed the plugs and leads but no change. Never come across this problam before, any help is much appreciated.

Cheers, Ed.