Part throttle misfire on Xantia 3.0

[Stempy]

When accelerating, especially before the engines warm, there is a pronounced stutter. I can't seem to make out if it's a misfiring engine or the gearbox throwing a wobbly. I guess if the engine was misfiring it could cause the gearbox to be a bit random. It appears to be at lower revs and part throttle, above 2500rpm it's smooth. I've watched the tacho which seems to stay constant. Trouble is it doesn't always do it which makes tracing the cause all that more difficult.