Lumpy idle?

I've noticed that our Scout (2010 2.0 TDI CR, 3 years old in September) is developing something of a lumpy idle when cold.

Seems to drive perfectly fine otherwise, just sounds a bit... "clonky" (to use a technical term) when you first start it up.

Any suggestions? It doesn't normally use much oil, but I'll check it tomorrow to make sure.

We're off on a long tour around Central Europe next month, so I don't want it it breaking down in the Czech Republic; but at least we should be able to get parts quickly!

It needs to go to the dealer to get some corrosion under the front edge of the bonnet looked at anyway; is there anything else we should get them to check while it's there?