Dreaded P0171 code solved

I have a 2002 Toyota Tacoma, V6, 3.4L, 5VZFE engine,265k miles. It's been giving me code P0171 for a month or more, and upon resetting, the code would reappear in a couple of drive cycles. The OBD freeze frame data always showed long fuel trim abnormally approx. 25+ (high).

The MAF (mass air flow sensor, original Denso) was cleaned with a qtip and sensor cleaner. I cleaned the both the large obvious sensor and the two small ones that were somewhat inside the MAF. All three had a thin dark coating.

I took before and after cleaning data at two rpms.

rpm, , Before g/sec, After g/sec
950, , 5.35, , 5.67
2300, , 11.91, , 13.79


I've driven about 15 drive cycles and the code has not reappeared !! It doesn't take much of a reduction in maf sensitivity to generate a code. The maf sensor was further from normal at higher rpms.

Hope that this helps someone. (of course, there are many other reasons for p0171 code)

 

Just to add I have personally not had good luck cleaning MAF sensors. Usually, I will get it to read right for a couple of miles but then it acts up again. At hot idle you are looking for your engine displacement in grams/sec. So for a 3.4 your idle value should be around 3.4 grams/sec.

 

Yeah, I had one of these for a pretty long time.
Turned out to be a combination of leaky intake and intake plenum gaskets.
I used a smoke machine I got off ebay but I could never really tell where the smoke was coming from so I sprayed soapy water all over the engine.
I was able to locate the leaks that way.