just reading through my G60 seems to run ok ish, but i dont run a lamba sensor, never have so i would guess that wouldnt be your problem. its not the CO sensor in the intake pipe is it? should get around 400 ohms across pins 2-3 i cant remember the excat figures, but dubforce will. a blocked exhaust would give lack of power ect, tried disconnecting it as far up as possible?