bchicked,
I disagree with your basic premise, that is "I know these codes usually mean O2 sensors bad".
The one code means that the air fuel mixture is always lean when the engine is running and the other means that the engine's lean condition is constant and has been stored in continuous memory.
The diagnostic question to ask is, "is the lean condition real, or has the sensor(s) failed and is reporting a false lean condition?"
If both sensors have stopped "switching", from rich to lean and back, then that is generally a clear indication that the system is in fact running lean. Both O2 sensors do not usually fail at the same time.
However, very frequently I see two failed sensors. I believe that is because folks will operate their vehicle with one failed sensor and continue to drive it until the other sensor fails and the check engine light comes on, or other driveability problems start to occur.
So, to add to what Steve has said, check all your vacuum hose connections. Look for cracks or breaks at the connections. Look for any spots where the hose may have been rubbed through or burned through.
You can check for leaks at the manifold gasket by spraying carb cleaner, or WD-40, arround the gasket edge and watch for the fluid to be "sucked in".
Also check the "snorkle" from the air box to the throttle body for cracks or breaks in it. The crankcase ventilation tube that runs from the valley to the throttle body is difficult to check but also needs to be looked at. It gets a lot of heat and dries out and cracks.
If you do not find any vacuum leaks, then maybe you have two failed O-2 sensors. In doing the diagnostics on such a problem I would consider the facts of the situation.
If you came to me with a car with 120K miles and told me the O-2 sensors were new at 100K, I would suspect one sensor but both would be very unlikely.
But If both sensors were original, I would suspect both sensors had failed. In fact I would recommend both be changed before doing any further diagnostics because of the excess age of the sensors.
If both of your O-2 sensors are more than 60K miles old, replace them. Then continue your diagnostics, if that does not solve the problem.
A code regarding most of the sensors usually indicate that the sensor has failed, or the connection between the sensor and the computer is poor or has failed.
A few sensors, including the O-2 sensor and the temperature sensor, can be causing the code AND be sending the correct information. The question is then why is the sensor detecting a faulty condition, e.g. too rich or too lean, too hot or too cold, etc. thumb
rangerj
