MoT Failure - HC Emissions

[S7Paul]

I've had the Chim for about a year now. It was MoT'd just before I bought it, and it's just had it's first MoT under my ownership. Everything was OK except the HC emissions, which was way over the limit. The limit is 200, and it was generally fluctuating around the region of 400-600, though would go up into the 2-3000 range at 2500rpm. Admittedly the engine is a bit lumpy on tickover, but it's not really that noticeable and it still goes very well. I've taken the plugs out in the hope that one would be a different colour, but they all look pretty similar. Has anyone else had similar problems, or can anyone suggest probable causes. This is not the weather to be off the road!

[S7Paul]

I'm sure it was plenty hot enough, the fans were kicking in every couple of minutes during the tests. In fact, had it not been for the fans coming on, and the extra load causing the emissions to increase, it might have just scraped through.

[S7Paul]

The guy at the MoT centre said it was a misfire, which may well be true, though if that is the case I think it's done it since I got the car, as I haven't noticed any difference. The engine shakes a bit on tickover, which on reflection is another indication of a misfire, but I'd assumed they all do that. I'm intending to try a new set of plugs & leads anyway, even though the plugs look OK. Do the plug shrouds (extenders) often cause trouble (as a set of those is quite pricey)?