P0171 - System Too Lean Bank 1 - Page 2 - Toyota 4Runner Forum

thegipper · 12-31-2020, 09:38 AM

Quote:

Originally Posted by clanofwolves

I did check for vacuum leaks first thing visually as well as using starter fluid, none detected.

The O2 sensors are original as far as I know, but wouldn't they too throw a code in addition to the P0171?

I remove and clean the MAF every 20,000 miles and I just did it about 5K ago, but maybe it is an issue anyway?

O2 sensors don't always throw a code when they go bad. If your O2 sensors are original, I'd replace them. It's likely the issue causing your P0171 and even if it isn't, they are due to be replaced. You'll probably pick up a mpg or two (I did when I replaced mine due to a P0172 too rich code).

Good luck

clanofwolves · 12-31-2020, 11:12 AM

Here is the data my Foxwell gives me at idle:

Bad Luck · 12-31-2020, 11:13 AM

Quote:

Originally Posted by clanofwolves

I did check for vacuum leaks first thing visually as well as using starter fluid, none detected.

The O2 sensors are original as far as I know, but wouldn't they too throw a code in addition to the P0171?

I remove and clean the MAF every 20,000 miles and I just did it about 5K ago, but maybe it is an issue anyway?

MAF sensor could be skewed and reading incorrectly even if it is clean. Same with the upstream oxygen sensor (air/fuel sensor). If it's readings are skewed, but it's still varying voltage you most likely won't set an oxygen sensor code.

FYI: Upstream oxygen (air/fuel) sensor tells the ecm the data necessary to adjust your fuel trims. The downstream oxygen sensor monitors catalytic converter efficiency.

Try to get live data after the engine has warmed up and the idle has dropped down to around 600 rpms +/-100 rpm

19963.4lsr5 · 12-31-2020, 11:40 AM

Quote:

Originally Posted by clanofwolves

Here is the data my Foxwell gives me at idle:

You need to repost the results after the engine is fully warmed up. Include rpm and TPS.

Try and switch your readings to American measurements if you can.

Sent from my iPhone using Tapatalk

jgue467 · 12-31-2020, 12:04 PM

My unit's p0171 was caused by the rubber hose just before the metal intake, replaced with new toyota OEM and all was good.

In my experience, 02 sensors throw a p420....

clanofwolves · 12-31-2020, 01:07 PM

Quote:

Originally Posted by 19963.4lsr5

You need to repost the results after the engine is fully warmed up. Include rpm and TPS.

Try and switch your readings to American measurements if you can.

Will do and will post.
Thanks!

LittleCaesar · 12-31-2020, 04:41 PM

At least with the preliminary data, not a vacuum leak and probably not a direct fuel problem. Most likely an aging sensor. Post the new data once you have it.

clanofwolves · 12-31-2020, 04:55 PM

Quote:

Originally Posted by 19963.4lsr5

You need to repost the results after the engine is fully warmed up. Include rpm and TPS. Try and switch your readings to American measurements if you can.

This better? What's it tell ya?

...again, thanks in advance!

Bad Luck · 12-31-2020, 05:19 PM

I would replace the oxygen sensors

19963.4lsr5 · 12-31-2020, 05:22 PM

Here is mine from this afternoon after a drive to the grocery store and back, sorry it’s upside down.

Sent from my iPhone using Tapatalk

LittleCaesar · 12-31-2020, 07:06 PM

+1 on changing out the 02 sensors.

Any drivability issues with the check light engine on?

clanofwolves · 01-01-2021, 12:16 PM

Quote:

Originally Posted by LittleCaesar

+1 on changing out the 02 sensors.

Any drivability issues with the check light engine on?

I'm going with the upstream O2 and see what it does. It seems to drive an accelerate fine, but she has stalled every once in a while when at a light with the AC on.

LittleCaesar · 01-01-2021, 02:54 PM

I would save your pennies and get both, but definitely replace the upstream if money is tight.

Ever cleaned the TB/IAC?

sroosma · 01-01-2021, 03:10 PM

I had this code right after I half-assed cleaning my MAF sensor. What I did was fully clean it and reset the ECU and it hasn't come back (that was months and a couple thousand kms ago). Not saying that it isn't the O2 sensor, by any means, but you may as well try and clean the MAF to see if that does anything before replacing parts. Probably best to clean TB/IAC while you're in there, too. good luck!

clanofwolves · 01-04-2021, 09:23 AM

Quote:

Originally Posted by LittleCaesar

I would save your pennies and get both, but definitely replace the upstream if money is tight.

Ever cleaned the TB/IAC?

I will on the O2s... I do some seafoam cleaning of the TB and I spray cleaner into the IAC when I am cleaning the MAF (the right brass screw is removed with a vice grip as the first attempted removal found her not budging, haha). I haven't paid an overwhelming amount of attention to the IAC, save I just insure she moves easily.

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