P0171 Lean bank 1 Question

[evaruni]

Hey all my 2002 sr5 has been throwing me the same p0171 code for about 2 weeks now, in addition to the CEL, the VSC and Traction control lights also come on, I’ve cleaned the MAF (however now I’m doubting whether I cleaned it enough) as well as changed my o2 and AF sensors then I reset the codes with my code reader and it stayed off for about 200 miles and has since come back, gonna try to get a new gas cap since it’s easy, will also clean the IAC and TB while I’m at it, any input would be greatly appreciated!

 

[RodrickHeffley]

Hey all my 2002 sr5 has been throwing me the same p0171 code for about 2 weeks now, in addition to the CEL, the VSC and Traction control lights also come on, I’ve cleaned the MAF (however now I’m doubting whether I cleaned it enough) as well as changed my o2 and AF sensors then I reset the codes with my code reader and it stayed off for about 200 miles and has since come back, gonna try to get a new gas cap since it’s easy, will also clean the IAC and TB while I’m at it, any input would be greatly appreciated!

When I had the 171 it was my MAF, gave it a good (dripping with cleaner fluid) clean with the stuff from O'Reillys and plugged it back in and it was all good, haven't had the CEL for nearly a year now.

It might be different on your 02 though as they changed the MAF after 98, but yeah deep cleaning it again can't hurt

Check for any vac leaks though, I had one around the same time that I'm sure didn't help the bad sensor readings

 

[hugho]

i have a 1999 4runner 3.4 4x4 automatic with 150k miles. my question is about this code p0171. it started 6 months ago, with the check engine light coming on and going off without being reset. just recently the light has came on , and is staying on. symptoms it has now is smell of fuel (mostly around tailpipe) and significant drop in mpg ( from 17/20 to 5/8 ) . I have cleaned the maf, replaced the maf with new, replaced fuel filter , replaced tps , fixed exhaust leaks, checked for vacuum leaks. currently i'm thinking about the upstream o2 sensor(because its cali emisions its refered to as a a/f sensor ) . it runs fine, idles normaly , no power loss , no hesitation . any help would be great.

I haven't read through all the posts but I had that code and an 02 sensor code on my first 4R. I didn't have a reader, the previous owner had it read. I cleaned the TB, the MAF and put in 2 02 sensors I got from Amazon which had the correct part numbers. It fixed nothing. CEL came right back on. I figured I'd need it scanned but the cost here was 50-$75 just to read it. F'get That! I decided to buy a proper scanner which happened to be on sale, an Xtool D7. It gave me the info I needed with reading the voltages, fuel trim numbers etc. The 02 sensors from Amazon were not doing their job. I decided to replace the upstream sensor, properly called an A/F Ratio sensor with OEM Toyota/Denso. More money of course but problem solved! No more CEL and even improved performance. I had thought this V6 was a bit of a dog but no more. When I did a month worth of maintenance I was smart enough to go all expensive OEM Toyota everything and have not looked back. I was too cheap to buy an OEM AF sensor and paid the price. You need a proper scan and I can assume you need a new AF sensor. There are other causes like leaks up stream on on the manifolds but the scan should help you to decide.

 

[dvachon]

i believe you are sincere - so allow me to comment. A few of these posts are a bit misleading and border BS. The one saying that the 5VZFE doesnt like the full K&N CAI is such a case and point.
The MAF installed in the CAI measures the air so the ECM can set the injection up with the proper fuel. As long as you can supply enough fuel to get a perfect AFR - YOU ARE GOLD. The engine runs off of fuel & air, atomized, timed, and injected.
And since I run one of those same CAI's myself - (along with the supercharger, larger injectors, and the Walbro pump) - like the URD kit that many others bought from Gadget as well - common sense should kick in.

The only time the P0171 code will be able to become the PITA it is now, is when the air fed into the mix is UNMEASURED.

In other words IF the O2 sensor is good and reading true - the "extra" air is getting in by a leak.
Else the MAF would be measuring it correctly and the ECM would set the injectors to match that air with fuel.
Since it is NOT - it got in illegally. Vac leak. Gasket leak. Anywhere the motor can suck it in - is suspect. The O2 sensor can only be blamed if it is giving a false indication to the ECM.

Even the K&N thing about their filter oiling fouling MAFs was debunked years ago and their proof is on YouTube, if you care to see it.

Personally, I have run both the drop-in and full monty CAI rigs and prefer the later. I wish you the best at killing the code. But ask that you use your own common sense. Obviously yours is more real than others in this battle - including at least one Toyota service tech!!

Cheers, thanks.