system too lean (bank 1)

I used a pocket scan code reader and got a PO171 system too lean reading. 2.7 liter 2001 eng. I don't know where too look from this point. Can anyone help?

 

check for air leaks from the throttle body to the air filter first

 

check your o2 sensors,bank 1 sensor 1 is your o2 sensor closest to the exhaust manifold,bank 1 sensor 2 is the the rear o2 sensor.You may just need to clean them or they may need replacing.

 

also check your mass air flow sensor,it might be just gummed up with oil and shit

 

yah true enough

 

X2

I had a 2000 w/ the V-6 that threw the same code. I was told to change the downstream O2 sensor to fix it, so I did. $85 later, still there. Turns out it was the MAF that was AFU. Look the directions here: http://www.4runners.org/writeups/throttle/index.html and try the MAF cleaning. It is a helluva lot cheaper than the O2 replacement. IF that doesn't fix it, you aren't out too much...and you have a clean MAF sensor! (I didn't know about this site back then...I paid a guy to diagnosis and fix it...that hurt)

 

My money is on a vacuum leak. My Honda Accord I had before the taco did the same thing. I drove around for six months on an expired tag trying to fix that damn code to pass emissions. After throwing many parts at it... Ended up being a vacuum leak.

 

mine started with that code so i first cleaned the maf sensor,didnt work,checked for leaks,same thing,replaced the maf sensor,still didnt work,replaced the o2 sensor and it cleared it. but now i need to replace the rear o2. lol

 

Dude, that is Murphy's Law! If you would have started the other way it would have been your MAF or a simple vacuum leak...

 

I got that same reading when my exhaust was leaking...

 

Be cautious on the O2 sensors, on most of the 2.7L bank 1 sensor 1 (nearest the exhaust manifold) is actually an air fuel ratio sensor. That went bad on my old taco and I got a no signal bank 1 sensor one code. I had a more advanced scan tool and I could look at the signal from that sensor to see if anyone was home.

If you are in doubt I would consult someone with a more advanced scan tool as I recall this senso being quite expensive ($150 +)

 

Thank you for all the suggestions. So far I've cleaned the MAF, changed the spark plugs (NGK bkr5eix 6341), cleaned the throttle body, and I am going change the fuel filter. I bought the O2 sensors but I'm waiting until I've tested everything out before I put those in. I'll give you the update soon.

 

Any update? Did this fix your problem or was it a vacuum leak?