Toyota Sensors

How to keep engine light permanently off after all sensors have been replaced, starter replaced, wires replaced, spark plugs replaced? Running lean keeps coming up on computer scan. Engine light has been reset numerous times. It has stayed off for 100 miles, 78 miles (twice), and today only 10 miles. Sometimes light will go out on its own and then later comes back on. What are my mechanic (33 years experience & race car driver) and I missing?

Toyota RAV 4, 1999, made in Japan. Car has to pass NY inspection during next 3 weeks.

Weather: upstate NY patterns

You’re putting the cart before the horse. The sensors aren’t the cause of the trouble codes. Their codes are the result of engine troubles!
You, and your mechanics, need to find the cause of the lean condition.

You might want to change the computer if the problem can’t be found. When that doesn’t work, you’ll want to find the cause of the problem. The first step is to find out what the code(s) are and then what the problem is. You did say lean condition which does sometimes get caused by the computer being insane, but there are other causes.

It sounds like the root cause of the problem has not been uncoverd such as fuel pump fuel inj. or air leaks and so on.

Running lean is due to two possible things, too little fuel or too much air. 90% of the time, this code comes up due to a vacuum leak. I’d look over every vacuum line you can find, then suspect the intake manifold gasket.

Good replys so far you may also want to check
Try search for lean condition- great site


There is another thread running which deals with a lean condition, OBD code 171. Though it’s on a Mazda, the ideas still apply.

The sensor which tells the engine computer how much air is going into the engine is the MAF sensor. The MAF sensor is dependent upon another sensor for correct operation: the intake air temperature sensor (iat). The iat sensor has to read correctly for the MAF sensor to read correctly.
The MAF sensor, and the iat sensor, can be checked with a digital multimeter. You can find the voltage values of the sensors in the repair manual, and in the articles linked to the “OBD CODE P0171” question.
The MAF sensor article:
The iat sensor article:

That is a common reaction to kill the messenger. While sensors can go bad, they are put on cars to sense when something else is going bad. Replacing the sensor will not help if the problem is what the sensor is sensing. Maybe it is time to find a mechanic who understands this.

Without the messenger, there can be no bad news. Wait a minuet! Without a messenger, there can be NO news!! Oh, woe! Woe!