More MAF woes...

[SammerP]

Hi guys, I wanted your expert opinions, I measured the resistance @ 4 Degrees Celsius and got 4.0 kOhms of resistance. This seems to be within spec? What do you guys think? I have the P0171 code but cleaned the MAF really well and cleared the code, still runs like crap for the first 10 minutes, then runs ok, then the check engine light comes back on.

 

[004Gunner]

I don't see how you figured that was in spec. Did you just figure out a ratio between temp and resistance? I would make certain that the ambient temperature is as close to the listed temperature as possible and test again. Did you rule out other causes of the P0171?

 

[SammerP]

I'm not sure what else could result in that code. Everything I've found points to the MAF. I'd love to know what else to troubleshoot.

You're correct that I assumed it was within spec as it read between the 20 degree and -20 degree specs, I guess I could wait a month until it's -20 here in Toronto. Hehe.

 

[004Gunner]

http://www.obd-codes.com/p0171 lists the MAF as the main cause but also mentions vacuum lines, the PCV valve, and fuel filter. Just let the MAF sensor sit inside for a while and test it there.

 

[SammerP]

FIXED! I took the Maf out and brought it inside. Checked the resistance, within spec for 20 Degrees Celcius. Checked the voltage and it fluctuates. The symptoms were so similar to so many MAF related posts that I took a closer look at the MAF I cleaned last week. Inside the tube are what look like two small resistors. They were really dirty. The How to I found online only talks about cleaning the air flow hole, and the wires. I stood the MAF up an UNLOADED a ton of carb cleaner into the thing. Did this about 4 times. The first 2 times the carb cleaner ran out black.

I want this post to end with a fix if people come across it. If you have a check engine light, gas mileage is down, and when you reset the computer it runs like crap for a while, then runs ok, then the light comes back on, clean the MAF, but really really really clean it. I thought I cleaned it well the other day, but deep inside is where the real cleaning is needed.

I laid rubber in the back alley after doing this, I didn't think that could happen.

Here's a link to the Writeup: 4Runners.org - Cleaning Your Throttle Body and MAF

 

[zcruiser]

I want to revive this old thread and reinforce SammerP's find because I also think most MAF cleaning misses this important point.

MAF cleaning instructions typically only address the wire that's easily viewed when checking the MAF. Here is a pic from the 4runners.org instructions:

In actuality, the thermal resistors are located down inside the tube close to the base, and you need to spray MAF cleaner down the tube to properly clean the resistors, not just around the outside of the tube.

I was throwing P0171 codes, did what I thought was the proper MAF cleaning and it returned. I took the MAF out again and took a closer look at it and that's when I observed the two resistors down inside the tube part of the sensor just like SammerP. Those are the things that need to be cleaned to get rid of P0171.