I have a problem with my car. It seems to run a little rich, rough and get poor mpg. It runs fine at wot and great when cold; no rough Idle. I am thinking it is the o2's because I have changed everything else. I did install some bosch sensors about one year ago. But I think they are the problem; can a sensor be working incorrectly and not throw a SES code?

 

Yes.

 

Ok I am going to start on it today. I did damage the top of the passenger side o2 when I jacked the motor up a while back, I have been avoiding the o2s because it is not going to be ease and I have no SES light. I already started to remove the passenger side header; bbk headers are no good if you want to change the o2 on the passenger side. Going with acdelco o2's this time.