Intermittent hesitation / misfire / fuel starve

[rheumatoid]

I have a Vectra Estate 120 cdti exclusiv (120) - 2006. Every so often and especially when cold I get something that feels like a misfire or very brief fuel starve. maybe only 0.5 secs. I know it probably can't be those things but its the best way I can describe it. I think it also happens most often at steady low speed. Dealer say it might be something to do with particulate filter regeneration but can't see that and wonder if I'm being fobbed off as they can't find anything and don't want a job to do under warranty.

Any ideas what it might be?

Thanks

R.

[rheumatoid]

sorry mods. just noticed this should prob be in technical. can you move pls.

Thanks