My 2001 Rav4 engine light keeps coming on. We had it hooked up to a computer and it said that it was "running lean". The suggestion was to change the spark plugs and the oxygen sensors. We have changed the spark plugs already, but now when the car is in a low idle (foot not on the gas at all) the car stalls. I don't know if that is a fuel problem or from the oxygen sensor. Also, where is the oxygen sensor or sensors? There are two "sensors" on the front of the exhaust manifold but I don't know what they are or if they are the oxygen sensors. Please help. If I can change a sensor myself to save some money, I would love to do it. If you think my stalling is from something else. I would love to know that as well. Thank you.

The ECU is reporting the cat error code because the O2 sensor(s) outputs are telling it so. This MIGHT be the O2 sensor(s). You say two sensors have been changed, If these were the O2 sensors, then there is another engine issue to fixed.

The usual reason is that the engine is passing excess hydrocarbons into the exhaust, typically because its burning oil due to exhaust valve guide wear or/and worn valve stem seals. For a 2001, you've probably done around 200,000 km, so valve guide wear is likely. A head recondition is the only cure if this is the case. If you see blue smoke on starting, that's burning oil.

Related issue is worn piston rings: also causes excessive oil consumption.

Another problem is leaking (ie dirty) injectors. Most garages can clean them.

Another problem is the engine is running too lean. This can be caused by a dirty air cleaner or any number of other issues.

SD

NO I WOULD NOT. IT WAS JUST A COINCIDENCE THAT THE LIGHT CAME ON. SOMETHING MUST HAVE JUST TRIGGERED THE LIGHT TO COME ON. IF THE LIGHT DOES COME BACK ONLY THEN WOULD YOU CHANGE THE SENSOR UNTIL THEN JUST KEEP DRIVING THE VEHICLE.

Could be anything...
Start by getting a scanner hooked up to see what the trouble code is, and then go from there. (Once the trouble is fixed, the light should go out on it's own.) Also, make sure the fuel cap is tight!

go back to the guy that rebuilt it and tell him your problem

2001 Buick LeSabre 3.8L V6 Check Engine Light come on after driving in 20 minutes,error code P0171.....O2 sensors and fuel filter changed ,how can I pinpoint the source.

A lean code can be caused by several different things. The most common, if you are getting a lean code on BOTH banks, is a dirty Mass Airflow Sensor (MAF) Cleaning the MAF usually fixes it.

If not, it could be caused by anything from a crack in a vacuum line to a bad fuel pump. (Anything that could make the engine run lean.)

Check for vacuum leaks. ie, vacuum lines them selves, the rubber tube that runs from the air filter to the throttle body. If it has a plastic intake manifold, possibly the rubber port seal gaskets between it and the engine. Lean codes are set when the PCM isn't monitoring all the air coming into the engine (vac leak) or low fuel pressure.

id do the plugs and an oil change at the same time

Most likely Mass Air Flow Sensor. Could be oxygen sensors also but the mass air flow is more common

NEED TO HAVE THE CODE PULLED FROM COMPUTER AND LETS GO FROM THERE