Right, the fact its on and off, but when you are driving along you arent fitting and removing the exhaust, is a pretty solid hint that its an intermittent fault somewhere not a problem with the exhaust.
My 3 best guesses are:
Coilpack
Loose plug lead on the coil pack
Injector
To test for those:
Coilpack just swap for a working one (feel free to bring it to a meet and try the one off of mine as you are local)
Loose pluglead should literally feel loose if its that, just take them all off the coilpack and refit and make sure they all click on firmly
If you plug it into an RS tuner it will tell you if its an injector (you can borrow mine if you like)
(or take it to Dan and he will do all of the above for you FOC by the sounds of it!)
Then once you have sorted the misfire its worth looking at remapping it.
Personally so far I have only really seen examples of Ktec not getting it quite right with mapping so I wouldnt advise anyone to go there myself as im not really confident they quite know what they are doing (although maybe thats just the fact that people make more noise if their car doesnt work than if it does so my experience may not be representative but its my experience none the less and hence all I can comment based on), if you want a custom map I'd go to MWM or RS Tuning but sadly both are miles away from you.
As an easy option I'd recommend the RS Tuner 98 RON map as one that will be a good match for your spec and at 80 quid you cant really complain that its not totally perfect. Mosely and Binny on here are fairly near you and both have it, im sure they would take you out to show you what it goes like.
My 3 best guesses are:
Coilpack
Loose plug lead on the coil pack
Injector
To test for those:
Coilpack just swap for a working one (feel free to bring it to a meet and try the one off of mine as you are local)
Loose pluglead should literally feel loose if its that, just take them all off the coilpack and refit and make sure they all click on firmly
If you plug it into an RS tuner it will tell you if its an injector (you can borrow mine if you like)
(or take it to Dan and he will do all of the above for you FOC by the sounds of it!)
Then once you have sorted the misfire its worth looking at remapping it.
Personally so far I have only really seen examples of Ktec not getting it quite right with mapping so I wouldnt advise anyone to go there myself as im not really confident they quite know what they are doing (although maybe thats just the fact that people make more noise if their car doesnt work than if it does so my experience may not be representative but its my experience none the less and hence all I can comment based on), if you want a custom map I'd go to MWM or RS Tuning but sadly both are miles away from you.
As an easy option I'd recommend the RS Tuner 98 RON map as one that will be a good match for your spec and at 80 quid you cant really complain that its not totally perfect. Mosely and Binny on here are fairly near you and both have it, im sure they would take you out to show you what it goes like.