Just had my cel flash and stay on again after i change my plugs, cos there was a misfire on no 1. But got in it before and the bloody thing gone of by itself. I was geeting a tappet like noise coming from under the intercooler when light was on, but not as bad now since igts gone off. is that the knock sensor retarding engine as i dont now what the knock sensor would sound like and where it came from?

 

I, and many others have had a problem with CEL and misfire on #1. I changed the reverse selection switch on the gearbox to fix mine; others have done the same.

This may, or may not be cause for you, but the cost to change was £50 or so and it may be worth doing to save you a lot of hassle. Try searching and you'll find a lot of posts on this.