Ok, so just got home and connected the Cobb to do some fault diagnosis and... Nothing. No fault codes whatsoever.
Now I'm stumped. Only other odd symptoms I've had before is that on two separate occasions the car felt like it was shaking up and down, almost like I was driving over bumpy ground with an equal frequency of bumps, except the car was sat still, idling. First time I thought maybe the road was built over a bridge that couldn't be seen from the road and cars going past the other way were shaking the bridge up and down slightly, but the second time it was on a bit of road that definitely isn't raised or anything. It's almost like an imbalance in the engine or something, but only happens very occasionally. That particular feeling has only occurred twice in almost 8 months of ownership.