Hey guys, I'm getting the above code right before my smog is due. I know I previously had issues with one of my 02 sensors but figured it wouldn't hurt to change both out. Only issue though is that I'm only showing one model for denso when I search Amazon. Is it the same part for both sensors or is each one different?

Also, say that's not the issue, what would your next check be? Or would it just be cheaper to get this fixed at a shop considering smog is coming up?

Sorry guys, I have a 99 v6 automatic in California

There are two possible answers to your question, depending on model & year.
So if you want accurate feedback, specify that in each post. Better yet, put it
in your signature.

This question has been asked hundreds of times. There's a sticky for the best
way to search: Sticky: Alternate Search for T4R - 3rd Gen Section

It might be cheaper to let a shop handle it if you can't diagnose it and start
throwing parts at it.

Source of 0171 on my '01 was air intake hose between MAF and plenum, use OEM parts they last far longer....

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Lots of different options for air/fuel and oxygen sensors depending on what you have. We need to know year/engine/transmission and if your 4Runner is a 96-00 we also need to know if it's Federal emissions (1 catalytic converter) or California emissions (2 catalytic converters).

As for the P0171 9 times out of 10 it's a vacuum leak of some kind which can be easily found. With the engine warmed up and running spray carb cleaner/brake cleaner onto the rubber intake pipes and vacuum hoses while listening for any change in engine rpm. Where you spray when the engine rpm changes is where your vacuum leak is.

Sorry about that, edited the post. I have a 99 v6 here in California. Anyone know a reliable and affordable mechanic they'd recommend in Riverside?

I had a P0171 earlier last year, I had a vac leak and that didn't fix it but I hit my MAF with some cleaner and that did the trick.

Where you are located does not indicate which emission system you have. You will need to either check the sticker under the hood or crawl underneath and count how many catalytic converters you have.

My lean code was due to someone putting the throttle body to the plenum gasket upside down.

The only way I found it was by putting a smoke machine on it.

This was after changing sensors, airbox, and hoses, and tightening every single hose clamp or doodad.

When you get a too lean code, most of the time it's due to a dirty MAF (Mass Air Flow) Sensor. The sensor wires over time build up dirt on them and don't give a correct reading to the ECU on how much air is entering the engine. It reads the air abnormally low, and thus reduces the fuel delivered and you then get a "Too Lean" condition that the upstream Air/Fuel or O2 sensor is picking up. Once you clean the MAF sensor, the ECU reads correctly how much air is entering the engine and the problem resolves itself.

I've had this CEL pop up twice on one of my 3rd Gens and both times a quick and easy cleaning of the MAF fixed it. Before trying to track down vacuum leaks, clean the MAF and clear the CEL. I bet it doesn't come back.

I did the same thing when I put my engine together.


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You didn't work on my 4runner did you? lol! Hey, it's easier than people think to put it in wrong ain't it?

They need arrows on the silly thing.

I dumbed upon it. I noticed the edge of the gasket not flush while looking for leaks. My MAF reading was lower on my rig at idle than my other 97 limited was. Spraying didn’t really make a difference until I unplugged the IAC so the computer couldn’t respond. Idle was still a perfect 750 in park and neutral and 600 in gear with the brake on.


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I have done this too. Drove me nuts.

All they had to do was make the top two bolt holes slightly further apart than the bottom two and it'd only go on one way. The problem is that they are a perfect square so one scratches their head trying to figure out what way it goes on...

I have had this problem more than once myself. I ran into this issue last September after a super dusty trip through the forest. I know from experience to check the MAF first when this code pops up. The part of the MAF that needs cleaning is the little brown bulb that's exposed. The 2 thermistors inside it are the IAT sensor circuit. I usually just use a q-tip and some rubbing alcohol to gently clean the bulb. It should be shiny. If it's dirty, it will have a dull appearance.

Hops this helps.

Cheers.

For anyone wanting to clean their MAF, this is a great example of how not to do it. Never use anything like a Q-tip which makes direct contact with the MAF to clean it, the sensor is very sensitive and can be easily damaged. Instead, use MAF cleaner which you spray on the sensor to clean it, and importantly will dry clean without leaving any residue on the sensor which can impact the readings.