P0171 running lean - Page 2 - Toyota 4Runner Forum

brillo_76 · 02-03-2023, 02:09 PM

Clean the MAF with only MAF cleaning solution in an aerosol can. Failure do to so will end up with nasty results. I always use brake cleaner or wd 40 to check for vacuum leaks those are easy to find being the engine will speed up when you hit the leaking area.

These are definitely old enough to have these vacuum lines cracking and splitting, especially the air intake pipes that come in from the air cleaner box.

mtbtim · 02-03-2023, 05:06 PM

Quote:

Originally Posted by Zhehan

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.

This is interesting. It was my understanding the wires inside were what you needed to clean off because those are what read the amount of air coming through.

Zhehan · 02-03-2023, 08:17 PM

Quote:

Originally Posted by Skulking

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.

Fine then!

Seriously though, I've never had an issue doing it this way...

But, noted that I'm doing it wrong.

gamefreakgc · 02-04-2023, 09:34 PM

Quote:

Originally Posted by Zhehan

Fine then!

Seriously though, I've never had an issue doing it this way...

But, noted that I'm doing it wrong.

Ha, you got a lot of flak for something that actually doesn't hurt anything! The amber-like bulb isn't the mass air flow sensor wires, it's the Intake Air Temperature (IAT) sensor. You can clean it with a q-tip as it's not fragile unless you apply significant pressure. The exposed wires coming out of the top are just to relay the voltage change based on temperature. Having the slight haze of dirt on it isn't a big deal either way though as your intake air doesn't really change temperature all that fast.

The two very thin wires tucked inside of the sensor is the actual MAF sensor wires. As they are very thin and hard to access anyway, MAF cleaner is sufficient as they are out of the direct flow of air don't get dirty all that fast. Those are the ones that should not be touched under any circumstance.

There are some things to be paranoid about and others not. You're doing it just fine.

Zhehan · 02-05-2023, 01:40 PM

Quote:

Originally Posted by gamefreakgc

Ha, you got a lot of flak for something that actually doesn't hurt anything! The amber-like bulb isn't the mass air flow sensor wires, it's the Intake Air Temperature (IAT) sensor. You can clean it with a q-tip as it's not fragile unless you apply significant pressure. The exposed wires coming out of the top are just to relay the voltage change based on temperature. Having the slight haze of dirt on it isn't a big deal either way though as your intake air doesn't really change temperature all that fast.

The two very thin wires tucked inside of the sensor is the actual MAF sensor wires. As they are very thin and hard to access anyway, MAF cleaner is sufficient as they are out of the direct flow of air don't get dirty all that fast. Those are the ones that should not be touched under any circumstance.

There are some things to be paranoid about and others not. You're doing it just fine.

I guess I had it backwards then. But, if I just clean the dirty bulb, the code will go away. And, I associate a thermistor with temperature...

Zhehan · 02-05-2023, 01:44 PM

Sorry this picture is so crappy, but it's a million years old and a screengrab I believe. But, as you can see, it illustrates the Intake Air Thermistor in our MAF. That's probably the source of my confusion.

gamefreakgc · 02-06-2023, 01:55 AM

Quote:

Originally Posted by Zhehan

Sorry this picture is so crappy, but it's a million years old and a screengrab I believe. But, as you can see, it illustrates the Intake Air Thermistor in our MAF. That's probably the source of my confusion.

It's all good. Besides, with a steady hand a lots of care you can do some things that are not supposed to be done.

For example, you'll search all over the forums that our idle speed cannot be adjusted and it controlled by only the ECU. Well, I adjusted my idle and all it takes is a little time and patience. Though once the factory paint mark is gone I was on my own if I could ever get it back to the way it was.

Point is, you're doing maintenance on your rig and learning along the way. Nothing wrong with that at all. The MAF is only about $50 if it gets totally screwed up anyway.

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