Thanks for the quick response, I didn't mean to imply the Kev mod was at fault I think it's just coincidence. I have checked the wiring and all is ok. I know the mod is working as the improvement is huge. I think a new plug will be my first stop as the problem is spluttering and mis firing, I just wanted to check I hadn't done anything stupid. There are no warning lights or fault codes so I assume its nothing to major. Thanks for the advice, I'll let you know when I find the problem.