I have had the P0171 code with my check engine light for about a month now.

Using CL forums I have replaced my spark plugs (NGK twin-ground), cleaned my throttle body, replaced the PCV hose, replaced the air-filter, cleaned the MAF sensor (didn't help) and changed it, still no help. Took out the fuel pump and visually inspected the 'sock' filter and it looked unclogged.

Car still bogs down upon heavy acceleration and idles rough at stops, especially when warm/engine is warm; worse after a drive and 10-15 minutes shut down to start up.

After exhausting the most common suggestions from this forum as stated above, I decided to take it in to Lexus of Louisville. I was there at around 1 pm and at about 330pm that's when they came up to me and said they were unable to diagnose what's wrong with the car and they will need an extra 2 hours, which will cost and extra $200. I told them I was not going to be able to do that but maybe make an appointment for another day. They pulled up my car, but then they still wanted me to pay $100. I refused because when I walked in I signed a contract that I will pay $100 for them to diagnose my car's CEL, and they didn't so what am I paying for?! Long story short, I refused to pay, and they refused to give me paperwork. I leave office but car won't even move now, 'dies' as soon as you put it in gear. Went back in argue until they called the tech who worked on my car, and he told me he took out the PCV valve to check it and it's working fine, checked for vacuum leaks but couldn't find any, took out the MAF sensor and cleaned it but it didn't help. He said after clearing the CEL it should take a few startups before car throws in a code and runs 'limp'.

His personal suggestion was to replace the oxygen sensors. Does it make sense that an oxygen sensor would throw this code..? I replaced the Bank 1 Sensor 1 oxygen sensor last fall, so if anything then it would have to be Bank 1 Sensor 2. Can anyone who understands the bigger picture and chain of events please chime in coz I don't know what else to do except my car right now is a gas guzzler!!

 

If MAF, fuel pump and filter, no vacuum leaks, PCV good, injectors not clogged, all are assumed good, the last thing left would be oxygen sensor.

 

Thanks for your input. Replace both on bank 1, or there is one of the two O2 sensors that is very likely to fool the computer into 'lean' error? Like i said, I replaced the upstream one last fall.

Also, would trying to use the O2 spacer/simulator help? I am now just trying to solve this for as little as possible considering the how much time and stress I've put in without success.

 

Did you ever find a solution to this problem? I am having the same exact issue and took it to a buddy (Lexus Tech) and he replaced the MAF and the computer said it was good and O2 sensors were reading good. On the way home it drove great, but on the way in to work this morning light came on and symptoms reappeared. And now my buddy left for vacation. Any other ideas? I have a SRT Intake, if that makes a difference.

 

Read my previous post

 

Actually, I haven't followed up on the issue since then. I've just been driving on it limping, but hope to get my tax refund this Friday and get it fixed. I will go for the 02 sensor per GS4_Fiend's recommendation. Not whining, but I am a single dad, who is not on welfare, and the bills leave me perpetually close to broke lol.

I will update with results, and good luck to you.

 

guys before you spend money on the 02 sensors, which I am not ruling out as the problem, make sure that your maf sensor is perfectly seated onto the intake. In other words go up to your MAF and make sure the O-ring is not visible and the sensor is sitting flush.

 

If you need a new maf, pm me i might have one laying around.

 

Not criticizing, but the code is for Lean Bank 1. If its both bank than the MAF sensor would be a part of the issue. Just saying.

 

Forgot to mention, a stuck open PCV will cause this situtation

 

FUEL PUMP was the culprit! Must have been going bad, but I can't complain at 273k miles Replaced it and now I'm back in business

I just hope I did not mess up my Cats coz there were times when I could smell the unburned gas. Only time will tell.

 

You got a gs3 or gs4? It would only make sense if it was a gs3, since it only has 1 bank.

 

It's a 99 GS300

 

The GS3 still has 2 banks. There is a front and rear bank. Front bank is cyl 1-3 and rear bank is 4-6

 

oxygen/air fuel sensors (in part) controls fuel trims, so yes they could cause a lean code.
id start with the MAF sensor, since that generally i've seen set this code. If that doesn't solve it, go for the oxygen/air fuel sensors, since thats the next logical step on the diagnostic process.