I have a 95 850, did the OBD1 read and it says I have a bad front O2. I had installed an A/F gauge and its ALWAYS reading rich, crappy gas milage too, all symptoms of a bad O2. Being on a very tight budget I snagged one from the junkyard, installed it, and nothing changed. I did the computer reset, and nothing...infact ill say its even worse milage then the O2 i removed. Im looking on eBay and see a universal Bosch O2 and know the Volvo OEM is Bosch, only difference is these don't have the connector already (read the part where I'm on a very tight budget)
Has anyone installed one of these and what was your results?

 

I have used a universal fit Bosch O2 sensor (where you splice the wires to use the old connector/wire extensions) with good success. I'd suggest you also check for vacuum leaks, ie vacuum lines, intake boots/tubes.

FCPEURO sells the universal Bosch sensor for about $61... You didn't mention if you have an NA or turbo engine. You may also need to check if your car's emission system has an air pump or not as that may change the part number for the O2 sensor.