Hi All, I've got a '97 STS with 122K miles on it. Been running fine for a few years, then all of a sudden last week she started misfiring awfully bad. I changed out plugs and wires and still misfiring though not as bad. And now I'm getting code PO138, something to do with O2 sensor. Does anyone know how to test this O2 sensor to see if I need a new one? My real question is where do I go from here? I'm mechanicaly capable and I would like to do it myself if I can.
Thanks. BTW there's some very knowledgeable people, I've learned a lot just from reading.