Since fuel trim is high at higher load and MAF reads ok for that load then suspect fuel delivery problem.
To verify post the fuel trims LT plus ST and MAF reading at idle normal operating temp.

 

could also be a oxygen sensor giving false readings

 

I bought a obd scanner and read the live data on the o2 bank 1 sensor 1. It's cycling between 2.6V to 3.4V at idle speed (after 20 mins drive). Is it in the normal range?

 

3.3v at idle is normal. If you do a snap throttle should go up to around 4.5v back down to arou nd 2v and then back to 3.3v.

Can you post the lt st fuel trims and maf at idle?

 

I'm not 100 percent what the voltage should be but I'd swap the upstream oxygen sensor with a denso unit. They can fail without causing a code in computer. My experience with the lean code is upstream oxygen sensor or maf sensor

 

When the ECM/PCM is having to add too much fuel based on input from the O2 sensor, the fault code P0171 will be sent to the ECM, which will trigger the check engine light to illuminate. This code could either mean that the oxygen sensor is detecting too much oxygen or too little fuel in the mixture. Check the air filter...

 

I'm assuming you're saying the engine air filter, checked this afternoon, looks pretty good, actually it was replaced last July.

 

I don't have the pictures for the fuel trims or MAF at idle, but I do remember some numbers, short fuel trims is -1 to 0, long fuel trims is 0 to 1, MAF at idle is about 3 g/s. As RPM doubled, the MAF is not doubled, but like 70-80% increase.

 

Ok, if fuel trims are increasing positive as engine load increases then suspect fuel delivery.

 

guys im telling yall from experience that maf can do this

 

Thanks to all of you, I guess we could rule out vacuum leak issue, correct? At idle, short/long term fuel trim numbers are not crazy.

 

Yes if fuel trims good at idle then vacuum leak normally not suspect.

Let us know what you come up with to fix the high positive trim under load.

 

Try some CataClean. You have a 2006 Camry and the catalytic converters are starting to clog. The Oxygen Sensors are most likely oxidized, holes are jammed with carbon deposits, and not able to send the correct info to the ECM / computer. Cataclean is Safe. Just do not get on the car paint, if you do get some soap and water wipe it off. If replacing Oxygen Sensor hope you have an O2 Sensor Socket, they cost $25 to $40. They have an open slot for the O2 wiring. With the car cold, not driven for a couple hours, you do not want to get burned. First, spray some Rust Penetrating oil/Lubricant (WD40 or other) around the base of the O2 Sensor and let soak in. If unable to remove O2 Sensor you may need to use a small propane torch, or heating clamp so you can loosen it from the socket. Be safe and careful. Never try to force it out as may break.

 

I started changing from the cheapest related parts, pcv valve, MAF sensor, looks like it works after the MAF sensor was replaced. Thanks to all of you.