That's why I was saying my kingdom for a scanner. A scanner would show you the "cross-over rate" (how quickly the voltage bounces back and forth across .445 volts) and let you assess potential health of the sensors. The 02 sensors DO get sluggish and DO wear out, but more often as not, are unnecessarily replaced as the "sentinals" bearing the news. "Shooting the messenger" if you will.
That said, it is possible the upstream sensor is the problem, it is equally probable it is merely reporting the news correctly. 02 sensors are located pre cat, and post cat. On the 93 there was one in each place. (newer Explorers have them on each bank for a total of 3 or 4). The one post cat is not going to tell you lean. It should remain flatline or close to flatline and its sole purpose is to monitor the performance of the cat. Your code would not be in any way related to thAT sensor in any way shape or form. Save your money and do not replace it right now. If you are inclined, the upstream sensor closest to the engine and pre-cat is the one your computer is getting the information from regarding the lean condition. If you suspect it, replace it. Like I said, I think your chances of it being the culprit, knowing only what we know at the moment are about 50/50.
Do you have a vacuum gauge? I'd be curious to know your vacuum readings.
Anyway if you plan to replace, just replace the one and let us know how it comes out. The good news is that even if it isn't "bad" they do age and replacement isn't ALL bad <smile>.
(I have 120K on one set and they are real healthy. I have 210K on another set, and they are getting a little sluggish, but are ok (I'd get better gas mileage if I replaced it).)
