I have a 91 300te 4matic. 205,000 miles. A little bit of rust, otherwise pretty sound.

An issue developed recently. It started as just a rough idle, that sounded like it wanted to die. It then started to die when I came off the throttle. It would usually start up again. After sometime it would be really hard to start, sometimes wait 5 min and it started right up and ran great. It then developed a check engine light. That would come on and then go away while driving. It would continue to drive quite well most of the time. I built a home made code reader I found on this site. I used it in the 16 pin code reader near the battery. Using Pin 3 it gave me a 17 blink code. Which told me faulty or grounded O2 sensor. So I think this is what is causing the CEL. I am not sure if I should just change it out or maybe change something with my fuel/air mixture? I am also wondering if this will fix my other issue. Does anyone know if the O2 sensor can cause a very rough idle and make it hard to start sometimes or did this come from something else going on in my engine. I have heard OVP Relay as well. I also checked vaccum lines and they all looked fine. I posted on another site and that seems to be the canned answer for this type of problem. This forum seems to be a lot more capable from reading many threads. Thanks for the help in advance.