slight idling problem (TD)

[TB2]

I went to munich and back last weekend going 150-160km/h mostly. Was a brilliant trip, though on the way back it happened to me (just 5 minutes after starting the return trip) that when I stopped at the red light, the engine stalled. I subsequently noticed how the revs went awfully low when breaking and coming to a halt. It seems like the critical moment is when the revs come down - it sort of swings to low and then stabilizes at maybe 850rpm. I don't thing the idle speed is too low in general. It's always been at around 850-900rpm and it feels right, but especially when breaking at a red light, going out of gear and with the HP pump kicking in, it's struggling not to stall.

Any simple way of fixing this?

Thanks!

[MULLEY]

Could it possibly be a slightly blocked fuel filter? I found that when changing gear, going down the box that is, if the revs dropped, the car stalled even though i was still moving.