I had this same problem and had some air getting by the prechambers. I bought new prechambers, rebuilt to spec injectors and new glow plugs. Now I was due so wasn't just throwing $$$ at it. My car has 227K on it and needed these items. It helped a lot. I still have some rough idle in very cold temps at initial start up, but overall the car is much, much better. I saw a post about adjusting idle on the IP too, but I am not familiar enough with the IP pumps and have heard way to many horror stories to be daring enough to try yet. Although mine is showing signs of beginning to leak so I will need to tackle at some point.