So i just bought this 98 taco. V6 5speed trd 4wd. It runs great, but out of nowhere i start getting a code p0171. So i search, i cleaned the maf 2 times with CRC electrical cleaner, the truck has new o2(s) from the previous owner. He told me he never had a code exept the O2s like a year ago ( seems to be an honest dude). I looked under the truck, i cannot find any exhaust leaks and there seems to be zero vacuum leaks.

Any ideas? Im baffled

TIA

 

Also this code only comes on on a slight hill doing 40-50mph.

 

Here is some help for you! How about a nice little trouble tree!

A. DTC P0171 - System Too Lean (Fuel Trim) has a number of causes. I'll run down the more likely possibilities and you can check them out in turn.

Air induction system. Any air leak between the Mass Air Flow sensor and the intake manifold will cause this DTC.
Injector blockage. You would need to do an injector balance test to determine which injector(s) are restricted.
Mass Air Flow Meter. This should throw a code. You can take it out and clean the inside with electronic switch cleaner.
Engine coolant temperature sensor. If the CTS is sending the wrong information to the PCM, it could cause the engine to run lean.
Low fuel pressure. You need to do a fuel pressure and volume test to check this possibility.
Leaky exhaust system. A leak in the exhaust system can dilute the exhaust gas resulting in a false reading.
Open or short in the O2 sensor wiring.
Bad O2 sensor.
A bad PCM.


(credit to about.com)

 

By the way I checked if there are any TSB's or recalls and there are none reguarding your current code.

 

I my opinion it needs an air flow sensor. It will probably be dirty with an oily residue. This will insulate the sensor and cause the computer to read incorrectly. Pull it out and inspect it, you can try to clean it, but the light will usually come back on. I have seen this repeatedly in the dealer.

 

I did clean it twice, i also did notice a bit of oily residue on the intake pipe (after the MAF) It also looked rather clean.

 

So i checked for intake leaks, i have none. I got the freeze frame data from two code pops today. One as 153 degree (truck wasnt fully warmed up so it makes sence) 2500 rpms 31% load 54mph. the other time 81% load 183 degrees and 3100 rpms @ 58 mph. the fuel trims where 19, 27 and -100% for 1,2 and 3 respectively.


Im getting really frustrated, should i just buy a new maf?

 

Gotta love that shotgun approach. You know there is a method to check the AF sensor based on RPM vs m/s air flow.


My advice is to diagnose the problem and not through parts at it. You've got a good place to start by using the trouble tree above.

 

What is this method you speak off?

 

Check out the FSM here.

Test for the MAF is here.

P0171 trouble shooting flow chart here.

 

P0171 System too Lean (Bank 1)

 

I had a 133 that turned into a 171 after I changed the front 02 sensor. Then the MAF tested out of tolerance (posted in another thread), so I changed that and updated to the 99-02 MAF/airbox. Still getting a 171 after warmup and back to idle. Pretty sure I have an exhaust leak at the cat flange, gonna see what I can do about that tomorrow. I'm crossing my fingers that is the fix but I'm not too confident.