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Old 06-15-2014, 09:13 PM   #1
Unabomber
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OMGHi2U Mass Air Flow Sensor (MAF) FAQ: Read as you know less than you think you do!

So what had happened was.....

I was cruising the interwebs on Facebook and I happen to be FB friends with Dominic Acia, lead tuner and office linebacker of www.turninconcepts.com fame. He made a posting there of results he had with a car on the dyno, before and after MAF replacement and it got me thinking....does Dom know something I don't and if I don't, then MOST Subaru owners won't as other than living in my mom's basement in my underwear, all I do is suck up NASIOC information and I've never heard of MAF issues by and large. So, I called up Famous Name Tuners 1-5 and axed them to verify and expound on what Dom had written and to the man they said, "That boy has his head screwed on straight!". Now that the background is set, here is some information that you should read fully and comprehend.

Here is what happens with an old/busted/dirty MAF in the real world:

https://i.imgur.com/waSnsAR.jpg

Green line is old MAF, Red line is new MAF. For those of you that don't know t00ning, this is a BIG difference!

OK, I'm sufficiently scared, so what do I need to do now? After combining the opinions of the five Famous Name Tuners, this is your recommended route: Clean your MAF often and replace it every 100,000 miles if it needs it or not.

Well how often do I clean it? There's some variance in opinion with this from yearly to every other oil change, but suffice it to say, if you have an oil impregnated air filter of one form or another, you should be erring on the side of sooner so you might be best off with every other oil change while the dry filter folks should do it yearly.

Well, how do I clean it? I'm glad you asked as I just did it with pictures as I'm a damned nice guy. Read carefully and don't do what I did as I screwed the pooch on this and went to maximum Jimmy Rustle on Father's Day.

Buy the supplies you need ahead of time as you may need them and if you don't have them, you have have much suck. Supplies are:
a. anti-seize (whatever flavor you like).
b. 2 new MAF screws. M4 by .7 is the size, length stock the internet says is 1" long, but yours may be shorter depending on the intake you have so buy several lengths as a 2 screw bag runs a whopping 60 cents at Home Depot. You can also get them with socket heads vice Phillips heads, but I'd not recommend those as its easier enough to strip/break the MAF with a screwdriver let alone with a ratchet. And if you think you won't need new MAF screws, I got news for you....you will. And you could always get these at the dealership if you wear a monocle.
c. New MAF O-ring. The size is 28mm id x 32mm o.d. x 2mm thick. Since this is just an air seal, there's not much need for exotic material, just a plain old O-ring will do. Should run you a whopping $1 in the real world, and $Texas at the dealership.
d. MAF cleaner. You can CRC MAF Cleaner, CRC Electrical Contact Cleaner (same as Item 1 only $2 cheaper), or non chlorinated brake cleaner.

You will need these parts because your stock stuff has likely given up the ghost and you are better off looking for them BEFORE the install than after. Ask me how I know....

https://i.imgur.com/yqkyI65.jpg

Here's the starting point. You, in a perfect world, only need a Phillips screwdriver, some MAF cleaner, and a MAF. If you look at the MAF, it has one super easy electrical connector you release with your thumb to free the wiring harness and 2 Phillips head screws to remove.

https://i.imgur.com/kDuVAl5.jpg

And here's a closeup of the MAF for those of you that don't know what a MAF looks like. Look closely at the top left screw...looks a little janky doesn't it? Janky screw head + McGilla Gorilla tightening + galvanic corrosion = Maximum Jimmy Rustle.

https://i.imgur.com/bRs99Cy.jpg

Here is the wiring harness popped off. This is actually one of the easiest wiring harnesses in the entire engine bay.

https://i.imgur.com/luXT13w.jpg

Son of a bitch! This is what happens when you strip a screwhead. I did this just to show the worst case scenario mind you, as in real life I would never strip a screwhead, but this is how you fix it correctly vice going nuts. Take a dremel tool with a small cutoff wheel and cut a " | " into the gnarled up screw head. You have just created a ghetto standard screwhead! If you attempt to drill the head off, which would work, the odds of you breaking the head off flush with the MAF tube are high. No flush = channel locks and twist it off. Flush = trying to EZ-out a tiny ass screw and/or helicoil the threads AKA a huge whore of a job. Mind you, the " | " will probably cut into the plastic MAF housing a bit, but its not much of a concern.

https://i.imgur.com/uHMjLTg.png

Now here is the MAF itself. The matchhead looking thing is the IAT probe and the MAF proper is hidden up inside tube. Spray up into the tube and let it drip down as the internet says immersion cleaning is not recommended. Spray these two parts and let dry a full 5 minutes. You can also spray the wiring harness connections, both on the car-side plug and maf plug.

You also see the O-ring. While you might get away with re-using it, odds are you won't and at a whopping $1, do the right thing. Mine was loosey-goosey and fell off and Home Depot nor Advance Auto had the correct one, but I did get one close at Advance and like horseshoes and hand grenades, close is good with O-rings. Slip a new one on and bonus points if you lube it up with silicone grease beforehand like I did.

https://i.imgur.com/9GMMTMC.jpg

Installation is reverse of how you took the dang ole thing off. These are the exact screws I ended up using. Remember...the length can differ depending on what intake you have. Use anti-seize to prevent galvanic corrosion + aid in your next cleaning. And these screws are holding a piece of plastic to metal, this is not the time to twist the on with the Wrath of Khan as you can break the plastic.

Well, how do I replace the dang ole thing? You have three options:

1. OEM. That jank will run you $200 or greater.
2. Denso 197-6040 on Amazon which should run you $120ish.
3. Janky eBay knock-off for $30. When I think about an eBay sourced MAF, this is how I feel:



All the tuners I spoke with said OEM is fine and most said the Denso unit was fine and/or had no experience with that part. eBay MAF....yeah.... Anyway, even with a replacement MAF, you'll likely need the same parts and remove/replace knowledge as denoted above in the cleaning process.

But I'm running a speed density tune, should I care about my MAF? Nope. The only thing you really care about is the matchhead thingy that does the temperature (which isn't a huge deal) and some cars run an aftermarket version of this, so if you are speed density, you just wasted 5 minutes of your life!

Should I reset my ECU after this? It is never a bad idea to perform an ECU reset after cleaning your MAF to clear out the AF learned trims based on a dirty MAF. The traditional route is to disconnect the negative battery terminal, press the brake pedal for a few seconds to bleed the system of charge, and reattach or you could do this via your engine management software.


Editors Note

This post was created due to my follow-up on the random musings of Dominic Acia of www.turninconcepts.com. I spoke with several other famous but anonymous tuners to corroborate the information and provide a group think version of cleaning and replacement schedule. My thanks to all!

If you find an error in this FAQ, please PM me with factual details and I will update this post. Responses such as, "You suck" or "I see you used a piece of janky blue silicone hose to quiet a rattling intercooler pipe in your inner fender" are not appreciated.
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Last edited by Unabomber; 03-28-2018 at 06:19 PM. Reason: fixed pics because good guy
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Old 06-15-2014, 09:13 PM   #2
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Placeholder in case.
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Old 06-15-2014, 09:16 PM   #3
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Thank again man!!! Another killer writeup!!!
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Old 06-15-2014, 09:20 PM   #4
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Wow, extremely informative, thanks!
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Old 06-15-2014, 09:32 PM   #5
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Yes finally something to back what i keep telling people. I always keep a spare MAF and rotate between the two
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Old 06-15-2014, 09:52 PM   #6
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Worth noting that many people clean just the IAT thinking that's the MAF sensor, the sensor wire itself is hair-thin and very hard to see inside the tube.
And cleaning the IAT really doesn't do much, it's a thermistor (thermally variable resistor) inside a sealed package and the actual element isn't exposed like the MAF is.
A quick way to check your IAT/coolant temp sensors for accuracy if you have access to a scanner with data monitoring- with the engine cold after sitting (preferably overnight), compare the readings from the two sensors. They should match within a few degrees of each other and read close to ambient temp. If one of them is way out of whack it should be replaced (this will usually be the coolant temp sensor since it's the one immersed in hot coolant).
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Old 06-15-2014, 10:08 PM   #7
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Quote:
Originally Posted by PSBeachBum View Post
Yes finally something to back what i keep telling people. I always keep a spare MAF and rotate between the two
You tell people always to keep a spare maf just in case?
Anyways good looks on the o-ring size. I have tried a thicker o ring, but after about 2 months, went to clean maf and the o ring had snapped as i was removing the maf sensor from the intake. Thank god it was daytime & i was able to see a portion of the o-ring still remained in the intake tube.
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Old 06-15-2014, 10:18 PM   #8
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I read this in the voice of dave chappelle.
https://www.youtube.com/watch?v=75XKGVwGEt4
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Old 06-15-2014, 10:37 PM   #9
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....i aint got TIME for no janky MAF....
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Old 06-15-2014, 11:40 PM   #10
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Excellent information! Thanks for doing the leg work!
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Old 06-15-2014, 11:59 PM   #11
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Quote:
Originally Posted by Unabomber View Post
does Dom know something I don't and if I don't, then MOST Subaru owners won't
Just keep telling yourself that. And we'll forget the eleventy posts a day you make talking out of your ass.
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Old 06-16-2014, 12:00 AM   #12
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Thanks to the wisdom of NASIOC and Unabomber, i've been cleaning the MAF every time I do the air filter.
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Old 06-16-2014, 12:16 AM   #13
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oh...the screws are JIS....and NOT phillips......which is why so many get FUBAR by n000000bs using the wrong screwdrivers on them


http://www.pentaxforums.com/forums/a...1-7-jis-sd-jpg
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Old 06-16-2014, 12:25 AM   #14
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Stick it! Or sticky, whatever. Well done!
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Old 06-16-2014, 12:27 AM   #15
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Awesome. Great Read. Thanks for the write up.
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Old 06-16-2014, 12:35 AM   #16
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Quote:
Originally Posted by Uncle Scotty View Post
oh...the screws are JIS....and NOT phillips......which is why so many get FUBAR by n000000bs using the wrong screwdrivers on them


http://www.pentaxforums.com/forums/a...1-7-jis-sd-jpg
Hmmmm......I guess you aren't as bad as I thought.
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Old 06-16-2014, 09:24 AM   #17
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Quote:
Originally Posted by Uncle Scotty View Post
oh...the screws are JIS....and NOT phillips......which is why so many get FUBAR by n000000bs using the wrong screwdrivers on them


http://www.pentaxforums.com/forums/a...1-7-jis-sd-jpg
I'm pretty sure mine were aftermarket so that blows everything out of the water. Are you sure if the OEM ones are JIS or not?
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Old 06-16-2014, 09:48 AM   #18
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Oh great now I can do this on my...oh wait that's right I sold my old wrx... Oh great I can still do this on my new wrx even though it only has 1000 miles!

But great right up thanks for the info!
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Old 06-16-2014, 09:50 AM   #19
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Quote:
Originally Posted by Unabomber View Post
I'm pretty sure mine were aftermarket so that blows everything out of the water. Are you sure if the OEM ones are JIS or not?
I cleaned mine on my bone-stock 2004 WRX wagon about 2 weeks ago, and unless someone before me had slightly stripped it out to a Phillips size or replaced it, mine was Phillips and not JIS.
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Old 06-16-2014, 06:31 PM   #20
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Quote:
Originally Posted by Uncle Scotty View Post
oh...the screws are JIS....and NOT phillips......which is why so many get FUBAR by n000000bs using the wrong screwdrivers on them


http://www.pentaxforums.com/forums/a...1-7-jis-sd-jpg

As a seasoned monocle wearer... http://www.amazon.com/Hozan-JIS-5-JIS-Screwdriver-Gen/dp/B003F63WI8

Also, haven't tried, but I expect these to take off the screwed in oil cover on the back of the engine under the flywheel. Got to be worth a few bucks not to be drilling those bastards out unnecessarily.
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Old 06-16-2014, 07:41 PM   #21
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Noob time.

Why does the AFR get wonky near redline with the new MAF? Seems like the old stayed more stable until redline/fuel cut/off-throttle? Did they just come off the gas sooner?
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Old 06-16-2014, 07:48 PM   #22
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Quote:
Originally Posted by kabz View Post
As a seasoned monocle wearer... Hozan JIS-5 JIS Screwdriver Set (NEW 3rd Gen.) - - Amazon.com


Also, haven't tried, but I expect these to take off the screwed in oil cover on the back of the engine under the flywheel. Got to be worth a few bucks not to be drilling those bastards out unnecessarily.

and the butterfly screws in the tgvs(ya GOTTA grind the end of the threads off first ) and tb too
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Old 06-16-2014, 07:51 PM   #23
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Quote:
Originally Posted by Unabomber View Post
I'm pretty sure mine were aftermarket so that blows everything out of the water. Are you sure if the OEM ones are JIS or not?
i know the 2.0's were....

if ya use a screwdriver outta a computer tool kit it will usually be all good..
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Old 06-17-2014, 07:31 AM   #24
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Ruuuuuuuuuudyyyyyy
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Old 06-17-2014, 11:34 AM   #25
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Great write up. Thanks
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