Hi all, I'm new here. My wife has had her 2001 S40 for a few years, but this is the first time we've had any trouble.

The car started running really rough and the CEL came on. I had the codes read and get the following:
PO131: O2 Sensor Bank 1 Sensor 1
PO171: System Lean
PO303: Cylinder 3 misfire
PO341: Camshaft Postition Sensor A Bank 1
PO139: Slow response bank 1 sensor 1

I'm not too sure about the descriptions of the last couple...the tech's handwriting kinda runs together at the end.

This happened all of the sudden. Was running fine on Friday for about 1/2 the way home, then started hesitating and bucking. I pulled over and it felt like it wanted to stall.
Do you think that there's one problem causing all the codes (i.e. bad O2 sensor)? Or do I have multiple issues?? Should I just start w/ replacing the O2 sensor? The plugs are BRAND new.

I've done some poking around on the boards and found things regarding a mass flow sensor, etc. But I haven't had to do anything to this car so far, so I don't know where everything is. I'm fairly mechanically inclined, I do most of the work on my own vehicle...

Thanks in advance for any help/insight you can give me!