p0171 and p0174, but STFT and O2 sensor voltage indicate rich exhaust? - ClubLexus - Lexus Forum Discussion

Go Back  ClubLexus - Lexus Forum Discussion > Lexus Model Forums > LS Models > LS - 3rd Gen (2001-2006)
p0171 and p0174, but STFT and O2 sensor voltage indicate rich exhaust? >

p0171 and p0174, but STFT and O2 sensor voltage indicate rich exhaust?

Notices
LS - 3rd Gen (2001-2006) Discussion topics related to the flagship Lexus LS430

p0171 and p0174, but STFT and O2 sensor voltage indicate rich exhaust?

Old 07-10-18, 05:43 PM
  #1  
LSLsLS430
Driver School Candidate
Thread Starter
 
Join Date: Jun 2018
Location: Texas
Posts: 2
Thanks: 0
Thanked 0 Times in 0 Posts
Default p0171 and p0174, but STFT and O2 sensor voltage indicate rich exhaust?

So I have a 2001 LS430 with 240k miles on it. Around September of last year, my CEL would turn on and off, and around December, it stayed on. I have p0171 and p0174 codes stored and pending, indicating both banks are running lean. Along with this, I began having acceleration issues, where if I tried to accelerate quickly the engine would speed up without increasing my speed, but after a second or two it would "catch" and I'd accelerate really quickly. I can usually accelerate slowly with no problems. But this is what my OBD2 scanner is showing:




O2 sensor 1 bank 1


O2 sensor 2 bank 1


O2 sensor 1 bank 2


O2 sensor 2 bank 2

Any ideas what's happening here? I've tried cleaning the MAF sensor with condensed air (which I've since learned is not always effectice) to no effect, and ran some techron through my fuel system, which gave a MINOR improvement. TIA

edit to add: there's no way that sensor 1 behavior on both banks is normal. Is it?

Last edited by LSLsLS430; 07-10-18 at 05:51 PM.
LSLsLS430 is offline  
Old 07-10-18, 05:47 PM
  #2  
BMW7_LS430
Lead Lap
 
BMW7_LS430's Avatar
 
Join Date: Mar 2009
Location: GA
Posts: 717
Thanked 27 Times in 24 Posts
Default

Have you already checked for vacuum leaks? Maybe throttle body gasket or intake manifold gasket.
BMW7_LS430 is offline  
Old 07-10-18, 06:31 PM
  #3  
LSLsLS430
Driver School Candidate
Thread Starter
 
Join Date: Jun 2018
Location: Texas
Posts: 2
Thanks: 0
Thanked 0 Times in 0 Posts
Default

Originally Posted by BMW7_LS430 View Post
Have you already checked for vacuum leaks? Maybe throttle body gasket or intake manifold gasket.
I haven't, how would that cause this particular issue? Not questioning your judgement, just trying to learn more about how my car works
LSLsLS430 is offline  
Old 07-10-18, 08:20 PM
  #4  
BMW7_LS430
Lead Lap
 
BMW7_LS430's Avatar
 
Join Date: Mar 2009
Location: GA
Posts: 717
Thanked 27 Times in 24 Posts
Default

If the banks are running lean that means either less fuel getting injected (less probable) or more air getting mixed (more probable). This more air has to come from somewhere and it could be either from throttle body, intake manifold gasket, or some hoses somewhere.
BMW7_LS430 is offline  
Old 07-11-18, 04:58 AM
  #5  
Legender
Lexus Champion
 
Legender's Avatar
 
Join Date: May 2010
Location: TX
Posts: 1,736
Thanked 47 Times in 46 Posts
Default

When's the last time you cleaned your MAF sensor? Had similar codes on my LS400 and found cleaning the heck out of the MAF cleared up the problem.
Could be worth a shot. Dirty MAF/poor readings could cause more air to be allowed into the system.
Legender is offline  
Old 07-11-18, 07:43 AM
  #6  
911LE
Pole Position
 
Join Date: Dec 2015
Location: Arizona
Posts: 384
Thanks: 0
Thanked 38 Times in 33 Posts
Default

Those O2 sensor readings are normal. The computer knows how to read them as all O2 readings swing up and down.
I'm guessing your MAF needs to be cleaned correctly. My car has the same symptoms and once I cleaned it it ran perfectly. If you watched the cleaning video recently you can remove the MAF for cleaning. Once it is out put the straw from the cleaner about 1/2" into the bottom of the black tube. Flood the sensor with cleaner until it runs clear. You can check your progress with a bright light by looking up inside and seeing the 2 sensing wires. Continue to spray short bursts until the wires are spotless. Do not touch the wires with anything except the liquid spray. Let it dry, reinstall, and go enjoy what will feel like a new car.
911LE is online now  
Old 07-11-18, 08:43 AM
  #7  
Legender
Lexus Champion
 
Legender's Avatar
 
Join Date: May 2010
Location: TX
Posts: 1,736
Thanked 47 Times in 46 Posts
Default

Plus one on the above... worked for me.
Legender is offline  
Old 07-11-18, 09:08 AM
  #8  
jayclapp
Lexus Champion
 
jayclapp's Avatar
 
Join Date: Oct 2007
Location: AZ
Posts: 2,218
Thanks: 0
Thanked 30 Times in 27 Posts
Default

I cleaned my MAF recently (134,000 miles) just because I thought I should, not that I had any noticeable problems with the car. It was easy to do and the MAF came out bright and shiny. I can't tell any difference in how the car runs, but I feel better that it was cleaned and is perfect.
jayclapp is offline  
Old 07-11-18, 12:02 PM
  #9  
911LE
Pole Position
 
Join Date: Dec 2015
Location: Arizona
Posts: 384
Thanks: 0
Thanked 38 Times in 33 Posts
Default

Mine was quite dirty at around 120k miles and it was throwing the lean mixture codes. Once I cleaned it the car ran like it had at least 30 more horsepower. A very noticeable difference and it would actually accelerate every time I pressed the accelerator, not just when it wanted to.
911LE is online now  


Thread Tools
Search this Thread
Quick Reply: p0171 and p0174, but STFT and O2 sensor voltage indicate rich exhaust?


Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

© 2018 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: