My 95 4runner with the 3.slow keeps getting slower. I replaced the O2 sensor and it works fine for a while till the sensor gets covered with "soot" and throws the code 26 (gas/air ratio rich). I clean it and it runs great till it fouls again. I do get a little white smoke when I start her and burns a little oil over time. Valves? Any idea what may be fouling the sensor???

 

White smoke may be the normal condensation symptom. If it smells like coolant, though, then there's an issue.

Could be the valve seals and/or rings are wearing out. Check the PCV valve for blow by. There's numerous other possibilities for an off fuel/air ratio, but start there first and rule things out one by one.

 

My coolant levels are fine so I doubt its the head gasket. I'll check the valves and rings for leaking, can't think of anything else that would cover the the o2 sensor with "soot"?!?

 

Running way too rich, maybe? Could be Satan, I suppose.