I have a2000 4 runner 3.4L that just popped on a P0171 code, just a few weeks after I got the transmission replaced. I'm sure it's just coincidence, but what do you guys think is the more likely culprit? Air Flow Meter or the Oxygen Sensors?? 152K miles and never been changed that I know of.
Truck seems to run fine, except for the tiniest bit of roughness at idle... barely even noticeable...

Thanks!

 

Most likely the 02 sensor, or A/F sensor if you have a 4 runner speced for CA emissions. For replacement, either a Denso or OEM sensor. Nothing else. Ever changed it before now?

Use the Search Engine here to find the correct way to clean the MAF.

 

Never replaced the O2 Sensors. I don't know if it's spec'd for CA emissions... How could I tell?
Thanks for the help!

 

my truck threw that code a couple of months ago. pull your mass air flow sensor. spray it with brake clean, dry it off and reset the light and you should be good

 

Do NOT use brake cleaner. Use Mass Air Flow sensor cleaner. Yes, they actually make it. You can buy it at any auto parts store.

Brake Cleaner is too harsh and can harm the sensor.

 

P0171 is an "Engine Lean" code - too much air or not enough gas getting into the engine (or sensors tricking the ECU into thinking this). Have you ever replaced the fuel filter (if you're high mileage and the answer is "no" it wouldn't be a bad idea just from a basic maintenance standpoint). Also, pop the hood with the engine running and listen for any vacuum leaks - it'll sound like a faint whistle or hissing..

 

also dont run out and buy a new o2 sensor or mass airflow sensor. I did both at the advice of 2 different shops who did diagnostic work. Nether fixed it.

 

I'm getting the P0171 code & CEL and I know its related to my MAF.

On my first 99 4Runner, the code came up shortly after I installed a K&N air filter. Cured with a cleaning.

Now, on my 2nd 99 Runner, I had a hesitation problem off the line but no CEL. I figured it was the MAF, so I cleaned it (in place) by spraying with MAF cleaner. I removed the filter, and used a mirror, light, could see the prongs but it was awkward.

The hesitation was cured but then came the CEL. I checked w OBD and its P0171. I have been running with my OBD unit connected so when the light comes on, I can clear the code. Over the holidays, I'll pull the MAF and properly clean it.

Serves me right for laziness.

Bruce

 

i have hesitation also. lots of it. it feels like the throttle is being controlled by traction control. it hesitates if i mash the pedal but as i let off, it feels like the power comes surging back. very strange.

when i reset my ecu, it bogs horribly for a few miles. the two places i took it to were wrong. im sure the answer is somewhere on yotatech but i just have not had the time to drill through the data.

 

OK, I pulled the MAF and cleaned it good with MAF cleaner and cleared the code, and (knock on wood) it hasn't come back yet with about 30 miles of driving. But when I start the truck in the mornings it cranks a long time before it actually starts. I thought maybe this was related to the P0171 code, but it's still there after the MAF cleaning.

Any other thoughts on this? It looks like the fuel filter was changed in 2006 at about 110,000 miles. Rig now has 153,000. The start issue has been there since I bought the truck in September. I'm thinking Fuel Pump??

 

I'm no expert, but I would think the fuel pump would be working or not... Hope you do keep up with this thread, having similar problems and would like to know if you find a fix for it!
Ive got a 99 4runner, had the P0171 code, was also taking quite a few cranks to start. Cleaned the MAF, engine light has not come on for a couple months now. Helped out with the starting issue, but still seems like it takes too long to start. Granted, I've got 220k on the beast and live in BFreezingE Alaska.
Also developed a problem with acceleration at 40 or 50 mph, shop says Throttle Position Sensor. Going to go through this spring and give it a good cleaning, check coils and plugs, already have new wires... Clean out throttle body real good and change out the fuel filter.

 

my 2000 taco popped a TPS at around 90k miles, intermittant CEL, drove it for 3 months like that with no decreased mileage or power like expected... they are not too expensive and takes about a minute to replace. think I paid $75 for an OEM one. bust out the Chilton or Haynes and test the resistance with your DMM and see if it is within spec or not.

I would recommend you change out the pre-cat O2 sensor every 75k miles or so, they are an expendable item and will rob your fuel economy and efficiency long before they will throw a code. they're $65-80 on URD's site... I put a new one in my 4Runner just because it had probably never been done (166k) and I'm not joking, I went from 16mpg up to 20mpg!!! I'm back down to 17.8 now but was highly impressed with the difference.

for the MAF, I use CRC electronic parts cleaner, available at any autoparts place, works awesome, not too expensive. 2 second spray and it's brown crusty to bright silver shiny again! don't hold the can too close though...

 

Are you guys who successfully elminated the CEL (relating to the P0171 code) after cleanng the MAF simply cancelling code using an OBD code reader or are you resetting the computer by disconnecting the battery?

My MAF now looks clean. I cancel code with code reader but CEL (P0171 again) keeps reappearing after about 20 miles.

The hesitation off the line was the reason I cleaned the MAF. Hesitation now eliminated.

Thanks,

Bruce

 

I had a buddy clear the code with an OBDII before I researched the problem and cleaned MAF... Of course it came back.
Just disconnected battery cable after cleaning. Might have to look into replacing the MAF or any number of other things recommended on this (awesome!) forum.

 

At last. Cleared code p0171, disconnected battery for 30 minutes, drove for an hour, several starts and stops. NO MORE CEL.

Bruce