Xsara 1.6 8v Lumpy Idle

[mattpc]

Missus's Xsara seems to have developed a lumpier than usual idle. It also tends to struggle to catch itself from stalling sometimes if the throttle is blips and it is left to return to idle. Previous owner StuartMcB told me when I bought it for her from him that it had a little modification that cured a stalling problem. This unit is pictured here. Originally it was yellow but it has gone black now and it looks like oil has got in there. You can see from the picture that there is some in the tube. Anyone got any ideas as I'm a bit clueless on this one and the search facility doesn't appear to be working today?