1999 4runner, P0171 code!

Hi all, I got this code (p0171) recently and am trying to isolate the problem. The acceleration is quite poor right now.

This far, I have tried the following, but the code keeps reappearing:
- cleaned the MAF censors
- replaced the fuel filter
- tested the pressure from the fuel pump, it is normal

I also pinched/blocked the return pipe from the fuel regulator and test drove the truck and it seems to be running fine with return pipe blocked. Right now I am open to suggestions about what it could be.

Also, if there is a diagram of fuel/vacuum system that I anyone has access to, it would really help if I can see it (from Toyota manuals or otherwise).

I would try the following in the order given:
1. Put some injector cleaner in a tank of gas and see if that helps.
2. Clean the MAF sensor (done)
3. Check the fuel pressure (regulator) and flow (filter).
4. Replace the coolant temperature sensor.
5. Replace the HO2 (A/F ratio) sensor in front of the cat. converter.
6. Replace the MAF sensor

From your experience with the blocked return line, it is likely that one of the above sensors is the problem.

just trying to pin-point the problem and save few bucks before opening my wallet to the dealership :grinno: I know they will go on replacing parts/sensors and pile it all up on me.

I put the list in the order I would do it in if I was paying for it.

In my 4Runner, cleaning the MAF meter did it.

Jheera_Blade

If you check the posts concerning my 1999 4Runner (4x4, 3.4L) you can probably fix yours too. After I replaced the #1 fuel injector everything seemed fine for a month or two so I figured that was the issue. Then, just yesterday the engine light came back on with the same code again. This time I will DEFINITELY take askwhy's advice and have the Air Flow Meter checked.

To see if one of the injectors is bad you can do several different tests. I had a mechanic do them because I was on vacation at the time but it shows you how to do it in my Hanes Manual. Give it a try and hopefully you won't spend that much $$$. The injector cost me about $150 from the dealer because no one had the item in stock. It took me just a few hours to take apart the top half of the engine to get to the injector rail and injectors. I had it easy because it was the #1 cylinder and it is located right up near the front of the vehicle. A lot of cuss words and some patience and I had it fixed and running again.

Anyway, good luck.

Mountain Biker from Texas