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Once the engine is warm, the 1st O2 sensor voltage should switch between 0.8v and about 1.2v - If it is switching to extremes (0v to 1v etc.) and the 2nd O2 sensor is reading low (about 0.4v ish) then you are probably looking at a faulty 1st O2 sensor.
I have experienced this on newer Renaults in the form of a Lean misfire (foot down, car hesitates and seems asthmatic). Usually seen in conjunction of the emissions light. New O2 sensor in this case works a treat.
Best of luck
Good evening, I hope I can help you.
What engine size do you have and do you have any 'P' codes from the code reader .
Hi again. First off all the front O2 sensor should as you say dance all over the place. It should vary between 0.2v and 0.8v. The rear sensor should be more stable with its reading of approx 0.7v.
Usually a misfire like yours, where you cannot determine what cylinder is at fault, eg removing plug leads and misfire doesnt change is normally caused by an air induction leak. You could try spraying WD40 around the manifold gasket area and vacuum hoses to see if that alters engine sound.