Hello All,

I've read numerous threads on the famous P0171 "system to lean bank 1" code. I too had this same problem. Running a K&N airfilter for 2 years, no issues. Cleaned MAF as recomended, put new O2 sensors in (both), reset the computer, comes back on at random. WHAT THE HECK right? Car runs perfect, stupid P0171...

Finally sucked it up and brought to the dealer (Toyota of HB). The technician boiled it down to a vacum leak around the throttle body, and wanted to know if I had any work done on the vehicle. OH CRAP! about 6/8 months ago I took off my throttle body and scrubbed and cleaned it using the same metal gasket but did not pay attention to how it was installed when I took it off. This just happens to be the same time that the P0171 monster was rearing it's ugly head. What a bone head move.
****Turns out the vacum leak was becuase I installed the gasket incorrectly on the TB. P0171 GONE!!!!

Figured this might be helpful to those whom are plagued by the P0171 code. It may not always be the MAF.

My truck is/was (sold it) 1996 Toyota Tacoma 4x4 V6

 

Ok, good to know.

 

You're right......P0171 is usually a MAF sensor but not always.
It can just as easily be a vacuum leak, O2 sensor, etc.