When I saw this, I thought you meant it was missing - like you had lost it somewhere.
Is it electrical do you think, or not getting enough fuel?
Take the plugs out and see what state they are in. If it has been missing for a while, they could be a bit cacked up. Clean them up as best you can, or bung some new ones in - only a couple of quid each.
Make sure all the earths to the Lumention power module are sound and clean. It only needs a bit of damp to get under one over Winter and you might be trying to earth through a rusty puddle. Usually though, Lumention either works or doesn't.
Does it start OK?
Will it rev when it is cold? i.e. is it simply a revving problem, or does it coincide with the engine running hot? Go out for a run until it starts missing. Stop. Put your hand on the coil. It should be "pleasantly warm". If it's boiling, it could be breaking up under load. Check it's securely mounted to clean metal. Check the wires going to it are not wobbling about. If it is very hot, fit a new one. £20 'ish.
How old are the plug leads? They can take on a lot of condensation in the damp and never recover.
Check the fuel filter is clean, and not full of rubbish and water. Is it new fuel, or 6 month old fuel?