All older engines start burning some oil. Your concern should be if the oil pump is working correctly or not. With engine idling, open the oil fill cap and look in...do this very slowly. Hopefully you don't have high pressure in your engine causing oil to actually come out the top with the cap open. If you do, then your pcv system needs cleaning/replaced, which could be the cause of this oil burn. If all is well with the oil fill cap off, look in and you'll see if oil is making it to the top of the engine or not. If it seems minimal,or not at all, then you've got dry engine parts working over-time, leading to burning oil and wearing engine parts...this is not good. Most likely reason is the "O" ring at the bottom of your oil pan which will require the oil pan off and the pump's "O" ring replaced. If this is not the cause, then engine ring wear and/or valves wearing is most likely the culprit. If your car is not sluggish (all you have is extra vibration) then I would live with this in regards to having to add oil, but you chouls check your top engine motor mount (the one off the firewall that is round with round rubber piece in it) to see if this is broken. These are easily replaced with a new poly mount which www.ipdusa.com sells as well as www.fcpgroton.com
Good luck!
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1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon. My cars have been running so well lately they've got me worried.