I posted a thread on a similar issue, bought a diagnostic lead off ebay which brought up misfire on cylinder 3. Only happens first couple of minutes when cold. Things I have tried are;
New coil on cylinder 3
New spark plugs
The problem is still there, looks like I should try and disconnect and clean the wiring loom, don't fancy that, who knows what will happen when I plug it back together!
I Just checked the colour of the old spark plugs, the ends are dark brown to black and the core is light brown. Don't know what that means, if anything.