What o2 sensors did you eventually fit? I looked at the price you said on your earlier question the other week and my sensors from Volvo cost £145GBP each which now is about $290 I think you stated about $165. You have the same problem that i had. OK, so i know each car acts differently, some may like the cheaper sensors but mine didn`t. The code also did not give any idea, it did at first when it went wrong but the cheaper spliced sensors were fitted at a local ordinary garage £50 each ,but i still had rough running and missing of cylinders with black smoke and 12 to the gallon but the o2 sensor code had gone. I suppose the code you have is still true, missing on cylinders, but does not point to the cause. It took me ages and another £350 to get it right by the proper Volvo dealer who put the sensors in. I hope for your sake it is the grounding earth wires, at least it will only cost you 2 star washers more!! Best Regards

Hello. I have run across the same problem before, one time it was a bad ground on the valve cover and engine block, the other time it was the cam sensor. My best guess is to check the large multi ground conn. by the rear knock sensor and just below. Take it off and insert a star lock washer under the conn. and tighten bolt. Take the ground off the left side of the valve cover near the oil fill and do the same. Report back. I may have other ideas. Pauli

http://www.brickboard.com/RWD/index.htm?id=1177594
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DanR