I had a local garage awhile back do a pcm scan and it said my driver's side o2 sensor was bad. Well I found out after taking the heads off, the driver side exhaust manifold gasket was broken causing an exhaust leak. Should I still replace the o2 sensor just to be safe while everything is apart? Is there anyway to test it to see if its still good? Also the motor has 120k miles on it completely stock, anything I should do while the heads/intake & exhaust manifolds are off?

 

As far as the oxygen sensor is concerned, with that many miles on it, i'd replace all of them. I just did a full exhaust swap, and got 4 new ones to make my OBDII happy. Plus it will save you some gas in mileage, and let the computer make more informed descisions on how to run the engine. Consider it routine maintainance

 

any recommended upgrades (<$500)? or does the motor have too many miles on it....