Nissan Repair: SES light, oxygen sensors, nissan maxima

Question
Hello, I have a 2000 Nissan Maxima GXE, with about 120k and my SES light comes on and goes off. I've had CPU diagnostic done (for free at Auto zone) and the results state the fuel is too lean. The code indicates to possibly replace the O2 sensor. I've had the Nissan dealership "supposidly" replace both O2 sensors on 2 previous seperate occasions when this light came on before, once at about 30k and again around 100k. I've also noticed over the recent year the car had been spark knocking intermittenly on acceloration. So I raised the octane from 89 to 93. Now, the repair shop I currently have researching it suspected it may be a loose hose causing the gas mixture to come up incorrect. But they cannot find anything and are not very sure what the real issue is. Do you have any suggestions on what I can do.  P.S Sorry I didn't have the exact diagnostic code on hand but I can provide if needed.  

Answer
Twan,

I would do a couple of things here first.  one go to high octain fuel and keep using it.  Lower octain fuel has more talc silica compounds that coat oxygen sensors and that is what kills them.  Second, get the throttle body cleaned and replace the air filter with a K&N and email me back with the results.  Rememer that your car has no conventional fuel filter and the only thing to do is when the pump goes is to change out the pump assembly, in the tank, that has the filter sock on it.  Now, did someone check the fuel pressure to see if the pump was good?