W204 C200 CDI Engine hunting on cold idle

[autocrazy]

Hi I own a '62' Reg Mercedes C200 CDI Manual (W204 facelift with Blue Efficiency diesel engine). My car has run 51,000 miles and only last week has done a 500 mile return trip without any drama (except for ABS-ESP light, which I have now taken advice from another thread and cleaned the ABS module contactor)

This morning when I started the car, the engine was hunting about 200 rpm from its idle value. This carried on over the next 2 mins when I stopped at a traffic light. I then gave the car a bit of a hard drive and reached the gym (3 miles later) and the idle only slightly erratic (the needle just flickered). When I returned an hour later from the gym and started the car it was fine and idled as it should at 800 rpm. I should stress there were no lights on the instrument cluster, so I do not think the car is recording any malfunction

What could be causing the car to hunt on a cold idle? Could it be fuel filter (this was the only item not replaced when I had the car serviced in May)

Thanks in advance for your help

[autocrazy]

This happened to me only once this week so far. It was the first time I used the car after about a week of being parked up after a straight 250 mile motorway drive. Wonder if that has anything to do with it (water condensation or sticky valve/ throttle flap???)