Volvo: 1999 S80, poor gas mileage, oxygen sensors

Question
RAY, COULD YOU PLEASE TELL ME WHAT KIND OF SYMPTOMS THE CAR WOULD HAVE IF THE OXYGEN SENSORS WERE IN FACT BAD ? THANKS AGAIN. SINCERELY PETE
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-----Question-----
My 1999 s80 has just hit a little over 100,000 miles. @ approximately . 62,000 ml. I was told that the lifters needed replacement after they had replaced the o-ring in oilpan was replaced since their was lifter noise. After agreeing and 8 weeks in garage was told that valve had gotten bent when installing lifters and so they had to reinstall. also replaced timing belt & spark plugs. was without car for so long and bringing car back on several occasions because very poor gas mileage ,very weak acceleration not to mention rough idle & sensor lights staying on. I was told that 02 sensors need to be replaced @ $200.00 ea. for a total of $800.00 & that was the reason for poor performance & lacking power. (the reason check emissions warning light)was staying on although it never came on before the work was done on my car. My car ran 100% better before I had allowed the garage to work on my car.Can you please shed some light on this for me ? I feel as though he just didn't install the lifters properly.Is that possible He also said he had too obtain a special tool for installation & a specialist to help assist him with the job. PLEASE HELP. Thank for any and all advise you can give me, Sincerely
         Peter F. Parent
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Peter,
Yes there are special tools that are needed when doing that job. If the tools were if fact used then the job should be done correctly. Now were those tool used? The tools are used to line up the camshafts when putting the engine back together, that keeps them in time. Ok now if the cams are in correctly are the front gears on right and the timing belt on and in time? Strangely enough the car runs poorly after that last repair. I would really suspect that the engine is not really lined up correctly. The fault codes that you are getting may indicate more as to what is happening. You may need to get to a shop that works on Volvo and has the proper test equipment to read the codes and make the right repairs. Now the lifter are straight forward and only go in one way and what we will call "idiot proof". Both exhaust and intake lifters are the same.

Answer
Peter,
Most times 02 sensors will leave runability codes in the system. They will give poor fuel mileage, possibly a sluggish running engine. However you need to see what codes are in the system to better say what affect they will have on a running engine. Most cars I see only has runability codes in the system and runs fine.