alright so I have little to NO knowledge of engines, i'll put that out there right now.

so my 96 4Runner (V6 2WD) threw a code this morning on the way to work, got it checked, and it reads

P0171 - Air/Fuel Mixture System Lean Bank 1

now from what ive been able to deduce so far that could be a flurry of problems... but the general code means theres not enough fuel burning in cylinder 1? or is there too much?

I was told I have an intake manifold leak (the gasket is worn out and theres a small amount of buildup around the seal) and ive been told it could be as easy as a spark plug..

any information beyond this would be really helpful guys!

ps, yes ive been trying google, but I was wondering if anyones had something like this come across them before while I ALSO search google for troubleshooting.

http://www.obd-codes.com/p0171

its bank 1 which on a V motor contains cylinder 1. it doesnt mean it is cylinder 1.


A code P0171 may mean that one or more of the following has happened:
The MAF (Mass Air Flow) Sensor is dirty or faulty Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
There could be a vacuum leak downstream of the MAF sensor
Possible cracked vacuum or PCV line/connection
Faulty or stuck open PCV valve
Failed or faulty oxygen sensor (bank 1, sensor 1)
Sticking/plugged or failed fuel injector
Low fuel pressure (possible plugged/dirty fuel filter!)
Exhaust leak between engine and first oxygen sensor

This is a good list


Does the engine have an audible miss? A bad spark plug or wire can cause one cylinder not to fire at all which the O2 sensor will see as a lean condition because the fuel and air charge for that cylinder is going past the sensor without igniting. This is much less likely than say, a vacuum leak. If Bank 2 is perfectly fine it can not be a vacuum leak that effects the entire intake manifold. It would have to be a gasket right at the sealing surface of the intake manifold and cylinder head.

thanks for the info guys, I was told it has a "slight miss" but honestly I can'te tell one way or another.

it also has a whistling noise after about 2600 rpm under normal-higher throttle output, and every once in a while it sounds like the whistle is sputtering. is that part of my problem or is that a whole other problem?

/e I also remembered today that about 3 weeks ago I accidentally unplugged the MAF (I'm pretty sure it was the maf) while the engine was running, and it shut the 4runner off, and when I started the 4runner it had an engine code, I did the 'ol reset the ecu by taking the battery terminal off trick...

the shop told me that's the only code this 4runner has thrown, is that because I reset the ecu by unplugging the battery and it wiped it's memory?

i'm also reading the MAF thing, I did just put a new k&n filter into it, one of the good reusable ones that was oiled, could it just be the maf?

This post was edited by superfinger on Aug 26 2016 09:36pm

Have you ever changed the ignition wires?

Whistling and sputtering sounds like a vacuum or exhaust leak. Oiled filters and MAF sensors don't play nice together either.

I've only owned the 4runner for 4 months, I haven't tried the plug wires yet.



thank you for thie information. I should've probably cleaned a lot of that oil off before I installed the filter..

alright awesome new development, started m 4runner up this morning, COMPLETE misfire, guessing it was cylinder 1, but once the engine warmed up the misfire went away, and the check engine light made a reappearance...

Pull the plugs

I should be able to do this after work. I have to pull the damn intake manifold to get to them though