Failed MOT on emissions, quite badly

first ever test, the cars not been on the road

I only suggest it because the symptoms (well, HC and CO) are very similar to what I had on the DS with what turned out to be a dodgy plug. It ran fine under load, but on idle one cylinder was just not quite doing what it should.

Of course that's an ancient engine with no sophistication - yours has lots more exciting ways to go wrong!

Ian

How "slightly" has it been tweaked? If the new cams are of a significantly different profile then your ECU will have no chance of fuelling the engine correctly and that would explain the crappy idle and high emissions.