I've been noticing a slight surging feeling in my 850 T5 lately. It seems to be more noticable when cruising at a constant speed, or when slowly accelerating, up a hill for example. There's no noticable movement on the tach, or any difference in the idle pitch, I can just feel it slightly. My Lambda (O2?) light came on a little while ago, but the surging happens when the car has warmed up, so I don't know if it's related. Anyone have any ideas?