I have a 99 xc70 with CEL on. The past few days the idle has been sketchy with puffs of dark exhaust upon starting. At highway speeds it is fine but low low speed it sputters. The exhaust is real strong now. I have gotten codes ECM 280A front o2 and ECM 4801 3 way CAT. The rear o2 sensor has bee replaced twice. It is at the shop now getting ready for her appointment tommorow. I am just trying to figure out if it is purely the Cat or is the MAF involved? And how did my car get so screwed up? We have another 99 xc70 same mileage also needing a front o2 sensor. We take good care of our cars. Is this unusual? Or is the luck of draw and part and partial of owning a volvo? Klaus, what is your take. Am I way beyond the possibility of just a vaccuum leak? Help!!