trainerdude

i've read all the threads on the check engine light and what to do but i'm kind of stuck. my CEL came on last week so i took it to a shop where they read the codes and it came back with a PO171 (running too lean). they checked the O2 sensors and we decided to just clean the MAF sensor and see what happened. after resetting the codes the light came back on a few days later. should i go ahead and replace the front O2 sensor? is it possible that this could be from using a K&N drop-in filter? what is my next step, i'd hate to spend the money on an O2 sensor and that not be the problem.
thanks for your help

trainerdude

any ideas?????

TacomaTRD

did you try this thread?

https://www.yotatech.com/forums/show...ighlight=PO171

boogyman

When I got that code, my mass airflow sensor (MAF) was REALLY dirty. check out the above thread on how to clean it.. it takes about 15 min.

in particular, here's a single post that has directions (check the internet for pics..)
https://www.yotatech.com/forums/show...85&postcount=5

hamstrungtaco

ususally a bad 02 sensor would cause it to run rich, i know sensor # 1 will

trainerdude

i've cleaned the MAF once already and the light came back on 3 days later. it's a 99 sport with 92K miles on it, should i replace the sensor? it seems to be running fine, even better since the MAF cleaning, but i have noticed a small decrease in gas mileage.
thanks

MTL_4runner

Most of the time it is the MAF which causes that code.
If you cleaned it already then get a used one at a junkyard from a 99-02 Tacoma or 4runner

trainerdude

i cleaned it again and put in an OEM airfilter and then reset the codes. i guess if that doesn't work i'll try to find a used MAF sensor.
thanks for your help

Fahrenheit 451

Ditching the K&N will likely be the cure. This sort of post comes up all the time with the frequent cure being eliminating the K&N as the oil on the filter cruds up the maf. It may be worth doing a quick clean of the air pipes, box, maf, throttle body, pretty much anything the K&N may have gotten oil onto to prevent it from reoccuring.
Just an opinion

Unhappy99

Did you clean just the IAT bulby thingy, or actually get down into the MAF hotwires?

https://www.yotatech.com/attachment....achmentid=1361
https://www.yotatech.com/attachment....achmentid=1362

Berrymans B12 Chemtool carb& choke cleaner works well for me. Have to clean mine every 6 months or so.

MTL_4runner

Follow this to be sure you cleaned it properly:
http://www.4x4wire.com/toyota/mainte...tenancep5.html