Lexus RX 330 Banks 1&2 too lean code

[Kurtatron]

First problem since I bought this car in 2024. I’m getting two codes. P0171 and P0174. Says banks 1 and 2 are running too lean.

I thought this might be a vacuum leak, but I sprayed carb cleaner fluid on all obvious spots and discerned no effect.

So I plugged in my code reader and found these fuel trims.

At idle I’m getting -8-10% for both banks. At higher rpm’s, the trims run positive for both banks around 7-12%.

I’d think if it were a vacuum leak, the trims would be positive at idle and closer to zero at higher rpm’s.

MAF looks ok, I think. I got up to 90g/s near wide open throttle, and I also got 4.4 at idle. Maybe it’s reading a little low?

What could be causing my codes? Please help.

 

[panthermike]

IIRC, often times it is a faulty MAF sensor on these. Was reading about a gentleman that tested his Ohm reading at only slightly high, but new sensor fixed it. Another thing to check would be the PCV system for leaks.

 

[GMBoy]

Quick test - UNPLUG the MAF and drive it. If the car runs better and not lean that is your problem.

 

[clinebarger]

Sounds like a MAF issue.

 

[14Accent]

Don't throw a MAF at it! Toyota MAF's are tough as nails.

Check the intake boots between the air box and the throttle body, ESPECIALLY the small one between the resonator and the throttle body. Oil residue soaks those boots and over the years degrades the rubber until it cracks, in addition to engine bay heat and general age. You need to completely remove the boots and spread the accordion to do a proper inspection, but I'd bet money that you'll find your issue there.

 

[SC Maintenance]

At idle I’m getting -8-10% for both banks. At higher rpm’s, the trims run positive for both banks around 7-12%.

I’d think if it were a vacuum leak, the trims would be positive at idle and closer to zero at higher rpm’s.

Is this a driveway test with no load?

Can you take it for a drive at constant speed, low load? If its a vacuum leak your long term trims under a constant load for a few minutes should move back closer to zero.

 

[Oliveoil2]

Change the MAF and see. It’s a logical first step.

 

[Egg_Head]

Any warranty?

 

[iCurious]

Clean the MAF sensor first see if there is any improvement.

On these vehicles with the Hot Wire type usually collects debris and dirt and gives erroneous readings.

 

[Marcozi]

Have the intake system professionally smoke tested.

 

[nthach]

I had a rich code on the Prius - cleaning the MAF fixed it after running the freeze frame data through Gemini. The funny part was the STFT trims did dive into the territory to set codes per Toyota but LTFT was within margin.

 

[dkryan]

I had a rich code on the Prius - cleaning the MAF fixed it after running the freeze frame data through Gemini. The funny part was the STFT trims did dive into the territory to set codes per Toyota but LTFT was within margin.

What exactly does that mean, please?

 

[D60]

First problem since I bought this car in 2024. I’m getting two codes. P0171 and P0174. Says banks 1 and 2 are running too lean.

I thought this might be a vacuum leak, but I sprayed carb cleaner fluid on all obvious spots and discerned no effect.

So I plugged in my code reader and found these fuel trims.

At idle I’m getting -8-10% for both banks. At higher rpm’s, the trims run positive for both banks around 7-12%.

I’d think if it were a vacuum leak, the trims would be positive at idle and closer to zero at higher rpm’s.

MAF looks ok, I think. I got up to 90g/s near wide open throttle, and I also got 4.4 at idle. Maybe it’s reading a little low?

What could be causing my codes? Please help.

Does it seem to run any differently?

I had a 2000 Taco 3.4 that was just generally down on power with no obvious explanation and no codes. I happened to look at MAF readings and they just seemed wrong -- exactly how escapes me now.

Eventually I replaced the MAF and it was instantly cured. Power was back and readings were where they should be.

THAT SAID, 2000 technology on a now-ancient 3.4 is light years away from a 2024 MY

 

[iCurious]

What exactly does that mean, please?

He asked AI to diagnose his vehicle.

 

[iCurious]

Does it seem to run any differently?

I had a 2000 Taco 3.4 that was just generally down on power with no obvious explanation and no codes. I happened to look at MAF readings and they just seemed wrong -- exactly how escapes me now.

Eventually I replaced the MAF and it was instantly cured. Power was back and readings were where they should be.

THAT SAID, 2000 technology on a now-ancient 3.4 is light years away from a 2024 MY

Perhaps you misunderstood, this is not a 2024 vehicle. He bought the vehicle in 2024. Toyota/Lexus with the 3.3L are 2006 and below. They use the Hot Wire type which commonly gets contaminated from dirty air filter.

 

[Kurtatron]

Is this a driveway test with no load?

Can you take it for a drive at constant speed, low load? If its a vacuum leak your long term trims under a constant load for a few minutes should move back closer to zero.

It was a stationary test.

I then took the vehicle on a freeway run. Values hovered around -4% with no load.

Weird thing is I saw some extreme spikes. Like up 14% for a split second.

Something I failed to mention is I had this same exact code 8 months ago. I couldn’t figure it out, so I reset the code and didn’t see anything until now.

The code is triggered at the same time as the VSC light, vehicle stability control light I think it’s called. Could they be linked? The VSC light came on this recent time also.

 

[SC Maintenance]

It was a stationary test.

I then took the vehicle on a freeway run. Values hovered around -4% with no load.

Weird thing is I saw some extreme spikes. Like up 14% for a split second.

Something I failed to mention is I had this same exact code 8 months ago. I couldn’t figure it out, so I reset the code and didn’t see anything until now.

The code is triggered at the same time as the VSC light, vehicle stability control light I think it’s called. Could they be linked? The VSC light came on this recent time also.

A couple things, none definitive.

-4% trims are pretty much considered perfect - with +/-5% perfect and +/-10% acceptable. You won't get a code until I believe 20 or 25% - I can't remember which.

Given your running negative trims at sustainted speed still I would agree its unlikely a vacuum leak. Vacuum leak should show positive trims (adding fuel for the unmetered air)

I assume VSC is Vehicle Stability Control - or is in Nissan land. I can't see them being related unless its a shared wiring / ground issue.

Rich/lean codes are normally trigged by LTFT. I have never seen it but supposedly a very erratic STFT will also trip the same code.

I would clean the MAF sensor with the proper MAF cleaner, and then clean the MAF connector with proper connector cleaner, and try again.

I would also check your wiring on the A/F or primary 02 sensor to make sure you don't have something shorting out there. Erratic behavior on the control side is often wiring or electrical failure.

 

[GSCJR]

The code is triggered at the same time as the VSC light, vehicle stability control light I think it’s called. Could they be linked? The VSC light came on this recent time also.

This is by default, the VSC is disabled when the CEL illuminates. I second the suggestion to have a smoke test done to rule out any intake system leaks first; good luck!

I just put our 2010 up for sale yesterday; not a lick of trouble, but I think it's time to let go:

 

[D60]

The code is triggered at the same time as the VSC light, vehicle stability control light I think it’s called. Could they be linked? The VSC light came on this recent time also.

Yep, we've decided if anything is wrong with the power train we can't use advanced safety features.

I mean I mostly get it -- and I don't really want advanced safety features -- but it makes for quite a Christmas tree of lights just because of a flakey MAF, ECT, transmission solenoid etc

Subaru will light up every Eyesight and ABS, BRAKE light etc just for a transmission solenoid (don't ask how I know)

 

[GSCJR]

Agreed @D60. You can imagine what I thought for just a millisecond, when my cluster lit up for the first time on my Legacy.