Small turbo.

Today my car started acting quite strangely in town. I was driving coming up to roundabouts / traffic lights and the idle was momentarly dropping down, to cut out level of the engine, a couple of times the ignition lights flicked on but it didnt cut out, it instantly idles again at 900 rpm or so but is slightly erattic.
The car is driving fine otherwise.
Any ideas at what i need to replace would be great guys before i spend time investigating in the cold