How to Fix P0171 System to Lean Code

[speedgoat]

So my check engine light keeps coming on and storing a P0171 code for System to Lean. If I clear the light it just comes back on again within a couple of hundred miles.
The truck runs great. Last weekend I got 22mpg on a 250 mile trip. Any suggestions on what to check to fix this?

2000 Toyota 4Runner V6

 

[mark3406e]

So my check engine light keeps coming on and storing a P0171 code for System to Lean. If I clear the light it just comes back on again within a couple of hundred miles.
The truck runs great. Last weekend I got 22mpg on a 250 mile trip. Any suggestions on what to check to fix this?

2000 Toyota 4Runner V6

Do a search its a common code, have been through it myself. Start with cleaning your MAF sensor and make sure you dont have any vacuum leaks.

 

[rajuncajun]

Have you done the deck plate mod?

 

[d-k]

I just went through this. It was the maf sensor.
I tried cleaning it but that did not help. I replaced it
And now im all good.

 

[rajuncajun]

After I did the deck plate mod, I started getting this code at WOT.
I cleaned the maf 3 times. With a few days in between each cleaning and haven't seen the code since.

 

[speedgoat]

No I have not done the deck plate mod, all stock. I'll try cleaning the maf sensor. Thanks for the suggestions.

 

[PitbullRescuer]

I have this too. Cleaned the sh*t out of the MAF, still there. Try replacing vacuum lines first because it's cheap to do and a good idea regardless. If that doesn't work, replace the MAF. I'm plan on tackling mine this weekend.

 

[THEREALTOR1]

I just threw this code last week. I went out and bought a downstream o2 sensor as i've already replaced the upstream (a/f) o2 sensor about 2 years ago so I figured the other might have gone. I tried just cleaning the maf while it was still in the airbox as it seems like they torqued those maf screws done to 100lbft from the factory and one started to strip, but i wasn't able to get it clean enough and it re-threw the code after about 10 miles.

I finally got a chance to rip it apart over the weekend. Pulled out the airbox and disconnected the ISR mod from the throttle body. Sprayed the heck out of the maf, really getting down in the tube and getting those 2 wires clean as others have pointed out in some of the other threads in here. Cleaned the butterfly on the throttle body really good also as it had some black gunk built up on it.

Put it all back together and so far so good. Its been about 50 miles now and i've been clear, so anybody that gets this code, start with doing these 2 things first before spending any money on sensors or a new maf. Just be careful taking those screws out of the maf as I ended up stripping one. Had to pull the screw and the brass (female) insert that goes into the airbox out to get the maf off and with only having 1 good screw to go back in had to rig it with some electrical tape wrapped around the maf/airbox overtop the 2nd screw to help secure it. Probably should hit the scews with some lube beforehand.

 

[MX4R]

Wife's matrix and my runner both through this same code within 1 week of each other.

-disconnected battery first, do this before you touch the MAF harness to avoid shorting it and to reset the ecu.
-blasted maf with qd cleaner, not carb or intake cleaner because I have seen them both still leave a residue.
-replaced Pcv, they were junk on both vehicles, one gunked shut the other gunked open.
-cleaned throttle body on both and reassembled.

Hundreds of miles on each and no stored or pending codes. Vac lines as mentioned is another good check. Also clogged fuel filter would cause a lean condition. FPR vac lines are another one. Basically it should be something simple, or a combo of simple things. And you'll get to check over a bunch of stuff that you should look at anyways.

 

[[email protected]]

P0171

Hi i have an issue where the code P0171 pops up on my 2001 toyota 4runner it has 155k miles , but vsc off and vsc trac light turn on when i scan it. i replaced the filter with a K&N air filter, and replaced the maf sensor and both upstream and down stream sensors. truck takes about 2-3 to start up but after it starts it idles normal.

anyone know what i can do next?

 

[spartacus]

vacuum leak after the maf since maf is new. Test the maf anyways. Check the vacuum hoses are good. Replace the gasket on oil filler cap and fuel filler cap.
Valve covers good.

maf test
How do you test if MAF is ok?

 

[jgue467]

Sometimes the large 'hose' next to plenum develops cracks along the folds, can be hard to see yet they leak. Replaced mine and 0171 is gone for years now. Luck finding that leak, spray some intake cleaner until idle changes to find it.

 

[gtfour43]

Had the same code for a while. Turned out to be the vacuum cap at the rear of the throttle body. This was on my 01.

 

[octanejunkie]

Sometimes the large 'hose' next to plenum develops cracks along the folds, can be hard to see yet they leak. Replaced mine and 0171 is gone for years now. Luck finding that leak, spray some intake cleaner until idle changes to find it.

I replaced that guy too, same reason

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