I have a "code PO172, rich or lean condition on one bank only, fuel trim bank one condition." I checked the plugs, and they were new, like the seller told me, but they were aftermarket Bosch plugs. Many parts on the car have been replaced. It looks like most of the vacuum lines were replaced and I would not be surprised if the O sensor was replaced, probably w/ aftermarket only because of what I observed with the plugs. So I guess I either have a vacuum leak(s), a bad O sensor, or an aftermarket O sensor that is as good as bad. Does this code, PO172 differentiate between these defects? I looked for the charcoal canister but could not find it. The vacuum lines under the battery box look new.

Also, there is a timing belt sticker, not Volvo, but GATES, and the seller told me he changed the belt but not the tensioner or rollers. When I did my '98 the first time I only did the belt;the second time I did everything, but the car was not 13 yrs old. Do you think I should change the tensioner and the rollers?

I took a chance w/ this car because I needed a car in a hurry, knew the car was not perfect but like the model and year as I have one. The seller has been very cooperative and so far everything he has told me has checked out. He already replaced the ABS unit and gave me the bill of sale w/ guarantee. I am going back to see him tomorrow and the more info I have the better he will be able to help me. Thanks again for your help and anything you can add is appreciated.