Well, I replaced the resistor in the secondary O2 sensor and the light stayed off for about a week and now back on again. Last time it was off for a few months...weird. Must have been a fluke or maybe that sensor really is going bad.

Anyway: It seemed as though, once I replaced the resistor, the car started opening the air pump valve again and pumping exhaust into the engine compartment on startup (I just cut the hoses and threw the pump away...didn't block off the valve). So that baffles me a little...

Now I found a nifty little switching resistor board that is supposed to read the primary (front) O2 sensor and send a similar signal to the ECM in place of the rear O2. Since I'm not getting any front O2 codes, this should send the reduced voltage signal to the rear sensor wires and the car should think the rear sensor is still hooked up. It's kind of a convoluted explanation, but it's called a psO2sim available from bakerelectronix for about $40 and I'll let you know if it really works and stays off for an extended period of time this go-round. If not, I'll be scrounging the junkyards to put a pump and hoses back in...