Hey thanks for the responses. I appreciate the feed back a lot. I do want to clarify a couple things, and then I will test out your suggestions and get back to you with what I find.
First, I do know that the EGR doesn't cause the PCM to go into closed loop (although I did think it was the coolant temperature sensor, not the o2 sensor that tells the PCM to go into closed loop). My understanding is just that the exhaust is cycled through the EGR more during open loop than during closed loop in an effort to burn some of the fuel that did not burn because the engine was still cold. But might be wrong. So I hypothesized in my earlier post that perhaps my car is over working the EGR (causing extra build up or something) because it is stuck in open loop. But I am open to any more sure ways of determining if I am stuck in open loop than my hypothesis based on limited understanding.
Second, I forgot to mention that when I first noticed the o2 sensor code (before parking the car) I did replace the o2 sensor. I think it was the upstream one, whichever one has only two wires and is accessible from the front of the car, under the hood, and it looks like it plugs into the front of the engine. But the code didn't go away in the 2-3 months that I drove it between replacing the sensor and parking the car. Part of me wonders if I should have replaced the downstream o2 sensor (although I was looking at that yesterday and it looks like a real pain to replace because mine looks rusted in place).
Finally, I've got a really simple code reader. Both of you suggested using a smarter one. Any suggestions on a cheap but effective option to get more info out of my PCM than the simple code reader I've got? Also, I was reading somewhere about gathering live data from the OBDII port and it sounded like not all vehicles can do live data, even if they have the OBDII system. My car is a '99 so it barely even has OBDII. I would hate to purchase an expensive diagnostic tool and find out it can't deliver live data. Should I be worried about that?
Again, thanks for the prompt responses. I'll try to get back to you on my progress fixing the EGR code.
Sunday, February 2nd, 2020 AT 8:18 PM