Thank you all in advance for your help.

I have a 2000 Es300 with 114k miles mostly hwy. It all started with a check engine light and code P0171 lean on Bank 1 right before I was going to do the 100K tuneup.

So I did the normal 100k tuneup

Plugs
belts all including timing
filters
oil
general clean up

The car is pretty clean being a California car that is garage kept. no leaks no problems.

Still I had this code p0171 kept coming back . From this forum I found that it was probably the O2 sensor and bank 1 was the one between the engine and the fire wall.

So I replaced it. 12 miles later and the lights were back on ( check engine & traction ). Figuring that I had made a mistake and replaced the wrong O2 sensor. I went back to the auto parts and bought the second O2 sensor and replaced it as well.

Still light keeps coming on

I have replaced

Both O2 sensors
new filters Air, oil, fuel
plugs
timing belt
cleaned the MAF
new Oil
and run a can of Berryman's fuel system cleaner

But cannot get this code to stay cleared. What am I missing???? Please help

Thank you and have a fabulous day

You mentioned you bought the O2 sensors at an auto parts store? What brand? You should be using factory O2 sensors, not a good track record with aftermarket parts.

The fuel system cleaner may have damaged the Fuel Pressure Regulator. If you have a manual and a vacuum youcan test it or visually inspect it for a micro leak.

I had the same code after running seafoam and loads of techron thru the system, it or both killed the FPR. swapped and all is well now and even passed smog with flying colors

Thanks for all of the Advice so far

I replaced the O2 sensors with Bosch 13540's . The dealer wanted X3 the price just could not take the hit. I almost always buy Toyota parts.

Can any one confirm what is Bank 1 ?

Also have Manuel but still not sure how to test fuel pressure regulator

Thanks again for all of your help

As long as you use the correct "direct fit" sensor you should be good to go. The Toyota sensors are also idle air sensors - so you must get the currect sensor.

I would look for any air leaks in the piping for the air filter or any other vacuum leaks. Any air leak will cause the lean condition ......... like a leaking intake manifold gasket.

Some have also reported getting the bank one with a bad MAF sensor -- but look for leaks before you replace parts.


Some of the aftermarket filters like K&A use oil in them and this is a known problem with some MAF sensors

The Bosch parts are supposedly direct replacement, I had the guy double check the the old part number to cross to the new one. I have been looking for vacuum leaks but have not found any yet. I have also be looking for an exhaust leak but have not found that either.

One other clue.....Maybe ???

It only happens sometimes when you are accelerating hard first gear it perfect but when it shiftes into second there is a lag or a loss of power around 3000-4000 sometimes the power comes back other times it is just slow acceleration.

Whenever you have a strange unexplained power loss taking a look at he converters is wise -- you could have a plugged converter on that side. The miles are high enough.

Hayne Manual will do, to test the FPR. Loss of power sure sounds like FPR.

I was chasing down a whole bunch of error codes due to the failed FPR, replaced coils, O2S,, almost everything then my buddy found my FPR was leaking, swapped and all is well, very well.

Bank 1 is the one facing the firewall. If the code is lean bank 1, then track any vacuum leak at bank 1, such as stuck open PCV, cracked PCV, check all vacuum lines on bank 1. The last resort would be oxygen sensor. But you said you already changed it so I'm assuming it's good.

Update

Replaced the fuel pressure regulator no change but now eliminated from the list of possibilities.

I borrowed a Snap on MT 2500 Scanner and a friend to watch it when I drove. We found that the air across the MAF was not constant and seemed low. Removed the MAF again and gave it another bath in MAF wash from CRC

It seems that the power has returned and the car runs much better but now getting a P0330 Knox sensor 2 malfunction.

Ideas?
Have a fabulous day

The saga Continues
I have done every thing above and i still cannot get rid of code P0330 knock sensor 2 malfunction

It only happens in the morning once I go over 60-65 MPH. I have tried warming up the car completely at an idle. driving smooth and easy. Starring later in the day but I cannot make it go away.

here is what it does

First drive out from an over night sit once i go over 60-65 on comes the lights. Reset the code and good for the rest of the day. I have done six different trips during the rest of the day covering 60+ miles driving hard, driving soft and nothing but the next day it starts all over like ground hog day.

Once I reset it for the day I can do anything. Driving that should make it fail and nothing. All of the normal performance, no lag, no issue

When the light come on i am generally cursing not accelerating at all. I am totally stumped

Is that like a personal assistant that does everything for you?