Worth getting your code reader out and checking the live misfire data for each cylinder. I cant remember the number of misfires allowed and over what period of time before a code is thrown, but I do recall it being very high on the AJV8.A few weeks back I'd started noticing a very slight miss on idle that wasn't always there, noticeable as a shake through the seat. I'd planned to get it looked at but a few days later whilst accelerating hard I got the flashing EML for 5 seconds or so and it ran badly as I nursed it home. This gave me P0304 and P1315 codes, took the car straight to Hoffmans in Henley who changed no 4 coil pack, much better but I can still notice this very slight miss on idle and I've had an infrequent stutter whilst accelerating, normally at motorway speeds with the gearbox in something like 6th rather than a lower gear and hard acceleration. Hoffmans investigated further but couldn't find anything amiss and it wasn't giving any more codes.