strange tick over

[Doofy]

Hi, My car seems to have picked up a strange habit,  Start the car cold, Tick over fine, Tick over when hot also fine, But its that point in between cold and fully warmed up the tick over is very lumpy, almost like its misfiring and vibrating. Had the timing belt replaced couple of months back but don't think its anything to do with that. tried different brand diesel,  but nothing helps, Nothing showing up on VCDS.. any ideas? Its driving me mad...

[Doofy]

No one have any experience of this?

[Doofy]

Scanned the car again today and got glow plug number 4 off, Can this be the cause of the engine running lumpy and sort of misfiring ??