Hi all,

Last fall I had to take the front down pipe (with front cats) off to have it re-welded. In doing so, I obviously had to take the 4 O2 sensors off. 2 were very difficult and had to soak with WD40. I got everything back on but within 2 days the engine light came on and has been on ever since. I bought a reader from Costco which told me there were O2 sensor issue in two different banks (forgive as I checked this 2 months ago and going on memory). The car has been running great up until friday. I was on a back road and punched it getting up to 80 or so but when I finally got down to idle speed the car idled VERY rough but seemed to run fine at 20mph or so when driving into the drive-in movie parking lot. After 6 hours of cool-down, the car is behaving normally. My question is.... How do you check an O2 sensor to tell if it's faulty. I'd hate to replace all 4 for only a couple bad ones. Does this sound like it could also be any other issue? Thanks ahead for your help!!!

Tyler