How do you tell if the mass air flow sensore is bad, or when it needs to be replaced. I have scaned the car (99 RX300) and the numbers I was getting for the long term trim is 43 and the short term is -3. does this mean that the mass air flow sensor is bad and needs to be replaced or can the problem be somerthing else. one more thing I have cleaned the sensor with contact cleaner, should i try brake cleaner? Thanks again......any and all ideas welcome.
Update: I cleaned it with brake cleaner and still no good. Light came back on. I also hooked up the scanner and noticed Bank 1 sensor 2 was at 0 volts until I gave the motor some gas then it went up but only to return to 0 back at idle. I really don't want to spend $150 on a new maf when it turns out to be an O2. There has to be a way to trouble shoot the problem better. Thank You for listening to me ramble. Ideas greatly appreciated.

 

I assume you have been getting this error repeatedly, not just one time, this is to make sure you are getting the correct trim numbers. I would actually reset the light first and then measure everything after a short drive of about 15 minutes.

1. Sometimes if you get a P0171, you get it by itself with no pending code, that happened to me last December, and I had other issues with my MAF, like some stuttering that I could tell was associated with it, put in a new one, and was set to go.

2. Contact cleaner is fine, but make sure you have cleaned not just the red diode but also the 2 wires inside the sensor.

3. Good, I see you are reading the numbers. Make sure you have tired to blow air into the MAF sensor (after removing it from its place) to see if voltage fluctuates.

4. On the MAF sensor, check the resistances against the following (hint after the drive the one at the very end (60C). If not within these ranges, you have a problem with your MAF

With ignition switch in ON position
Resistance: 13.6 to 18.4 at -20C(4F)
2.21 to 2.69 at 20C(68F)
0.49 to .67 at 60C(140F)

On that fuel trim that 43 is way out of bounds, should be no more than 25, but the -3 is within range.

5. As far as your A/F sensors, are you getting any code or just P0171, as I also have tested mine and gotten exactly what you describe, going up and then back to 0 at idle (my other uncle has one of those more advanced scanners). What are the higher numbers that you are reading off of those banks?

 

I am having no luck with this. I have replaced the mass air flow and all 6 spark plugs with original lexus parts and still the code comes back. I will post later with the fuel an o2 readings off the scanner. Any other ideas? Thank You for all your help.

 

These are all the possibilities:

Air intake (hose could be loose or a hole in one of the hoses)
Fuel injector (blocked, needs cleaning)
A/F sensor (check the readings to see if you are getting them)
MAF (I'll take it this is OK)
Engine Coolant Temperature sensor
Check to see if there are any cracks along the exhaust piping

 

Replace or check the Heated O2 Sensor, this particular O2 sensor regulates the fuel-air ratio in the engine.......