My V50 2.0D is teasing me during cruising, with or without cruise control. When the speed is being kept in the area of 1,500 and 1,800 rpm (independent of gear), the point where the car is between motor break and acceleration (hope it makes sense), it is unstable and jumping when trying to keep the speed without too much acceleration on a strait road. Of course no issue during clean motor break and nothing during acceleration through the mentioned rpm span.

Below and above the mentioned rpm: no issues at all.

 

Hi,
I have the same model I think, 2.0D 136HP.
Some time ago I have the same problems but it was because EGR failure.
After replace EGR valve all was ideal.
First check which you cold do yourself is disconnect egr wire, it will no cause any error, but disable actuating of valve.
If situation will be better then you got it.