I have an S-40 that my son drives and he has had some trouble lately with it and has taken it to one of the local Volvo shops (not the dealership) and had it worked on.They send it home , it runs good for a couple of days and then bad again. I have an S-80 and I bought a code reader since I do my own mechanic work and since he took it in now I can see what's going on to a minor extent. He is tired of the prices they charge for no longer than it says "fixed "so I would appreciate your help. Right now it's throwing a P0302 cylinder misfire 96.8 load, map 41.9 , 4944 rpm @ 72mph. It also shows P0015 exhaust cam over-retarded which has happened before, and P0130 o2 sensor 1 fault. while looking at the live data the o2 voltge was going from .03 to .950 in regular up and down waves . where should I begin to look? thanks

 

I would start with plugs,coils and both wires and go from there.