Mass Airflow Sensor
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This is a discussion on Mass Airflow Sensor within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; My 'check engine' light came on. I took my WRX to the local dealership. The first thing they asked me ...

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    Unhappy Mass Airflow Sensor

    My 'check engine' light came on. I took my WRX to the local dealership. The first thing they asked me was if I'd recently had the gas cap off. I told them I knew about that one and that my cap was on tight. Next they asked about my K&N air filter. I copped to that. Yeah, I have one installed. They tried to blame it on that. I told them that the check engine light didn't come on until at least 6 weeks after I installed the K&N filter. Next they said I needed a new Mass Airflow Sensor. Do you know how much those things cost? YIKES. I said that it didn't seem like a Subaru Mass Airflow Sensor should go out after only 60,000. So they cleaned it. Said that it was carbon buildup. And they reset the light. Three weeks later and the light is back on again.

    Before I pay a lot of money for a new Mass Airflow Sensor, does anyone out there have any input about this? Do WRX’s go through airflow sensors in just 60,000 mi? Is the dealership full of it? Or is a bad and terribly expensive sensor a real possibility?

    Thanks,

    Randy

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    Registered User GIRex's Avatar
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    Well i dont know very much about wrx's but i can comment on cars i have had with MAF's in the past. The miata would get a gunk on it, its either from a too oiled filter or just the stuff that is coming through the intake. I used a small amount of carb cleaner and compressed air to dry it faster. I worked well, if you use to much you can screw up the sensor. I have heard of filters messing up the sensor a lot, i have worked for a car dealership for over 2 years and they can refuse warrenty work for the aftermarket filter. it sucks and its bs but it can be a problem(higher flow ussually means more stuff can get through) if i were you i would upgrade to a MAP sensor instead.

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    Registered User BrandonWRX's Avatar
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    Quote Originally Posted by GIRex
    Well i dont know very much about wrx's but i can comment on cars i have had with MAF's in the past. The miata would get a gunk on it, its either from a too oiled filter or just the stuff that is coming through the intake. I used a small amount of carb cleaner and compressed air to dry it faster. I worked well, if you use to much you can screw up the sensor. I have heard of filters messing up the sensor a lot, i have worked for a car dealership for over 2 years and they can refuse warrenty work for the aftermarket filter. it sucks and its bs but it can be a problem(higher flow ussually means more stuff can get through) if i were you i would upgrade to a MAP sensor instead.
    Use non-chlorinated brake cleaner, it worked wonders on mine. But I think you misspoke on the MAP (manifold absolute pressure) sensor. The car already has one, it monitors the pressure of the air going into the intake manifold. The MAF measures the mass of the air, how dense it is.
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    Registered User STIBungy's Avatar
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    I know the VW MAF cost around $300. I had to call VW headquarters and was able to coax them into doing a goodfaith repair on my then gf's car.

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    Thumbs up Thanks!

    Excellent information. Thank you all.

    I suspect, given the above, that my new K&N filter is responsible. I haven't cleaned it, and so haven't re-oiled it. But I'm wondering if the oil that came on it could be the culprit. Maybe I should just go back to a Subaru filter.

    I'm assuming that if I clean up the sensor that the check engine light won't automatically go off. And I suppose that I'll have to buy some kind of gadget to reset it. Right? Either that or take it in for an expensive pit stop at the dealership. If there's a gadget - what is it?

    Thanks again.

    ~r

    P.S. the way that the board automatically adds similar threads is pretty cool.

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    Registered User GIRex's Avatar
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    you can buy cel readers and deleters off of ebay for much less than the hour of labor that the suby dealer will charge you. The link ECU gets rid of the maf sensor in the car and replaces is with a map sensor. so its not impossible i wouldnt know the first thing to do it but im sure some people around here might.

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    Registered User GIRex's Avatar
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    Im probably gonna get a perrin filter. i like the foam better but it will be a month or so before i get it.

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    Quote Originally Posted by GIRex
    you can buy cel readers and deleters off of ebay for much less than the hour of labor that the suby dealer will charge you. The link ECU gets rid of the maf sensor in the car and replaces is with a map sensor. so its not impossible i wouldnt know the first thing to do it but im sure some people around here might.
    So...they're called 'cel readers and deleters'? I'll look.

    'Link ECU' - I know what an 'ECU' is, but I'm lost re: a 'link' ECU.

    I think I miss the days of fiddling with Weber Carbs and installing new points.

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    Arrow K&N may = CEL

    …regardless of whether or not it was recently oiled. That may explain my CEL, because it’s new and hasn’t been re-oiled. So it’s hard to believe that a new K&N would dirty-up a MAF sensor. Since the MAF sensor measures air density, maybe the greater airflow confuses it – although the mechanic at the dealership said that the MAF sensor had carbon buildup. Gotta wonder were carbon would come from in that location though. Maybe I was following a diesel bus too closely. Sorry.

    Okay. Did some research. Lots of stuff to look at here at Club WRX. I appreciate all of the info collected here.

    Looks like I'll be buying an OBD-II so that I can pull and clear my own CEL codes.

    Also noticed that there are several references about K&N filters and CELs. Also noticed that if you're into monkeying around with 'tuning' the ECU that there seems to be a work-around for running an aftermarket air filter (as well as work-arounds for aftermarket anything else). But I'm not going there.

    I noted that there is an STI performance air filter. Maybe that'd be a better way to go. Anyone out there with experience with the STI performance air filter?

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    I Support ClubWRX
    I wrote a thread a while ago about the dirty MAF'ers

    ATTENTION!!! - K&N, ITG, Perrin Drop-in Air Filter Users

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    Thumbs up

    Quote Originally Posted by KurleeDaddeeWRX
    I wrote a thread a while ago about the dirty MAF'ers

    ATTENTION!!! - K&N, ITG, Perrin Drop-in Air Filter Users

    Awesome. You're the man. Thanks.

    ~r

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    Registered User AKESREX's Avatar
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    MAF and 301 code

    My 2002's in the shop right now for recurring CEL for PO301.
    After some online checking, the shop eventually stumbled
    onto a few technicians that have run across these issues
    and cleaning the MAF is what solved the issue. And that's
    exactly what the shop's doing to fix mine.
    BTW, my K&N's been on for about 60,000 miles and I had
    just cleaned and reoiled it at around 50,000. That's when
    I started getting the CEL. I changed the plugs initially, thinking
    that was the problem.

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    Quote Originally Posted by AKESREX
    My 2002's in the shop right now for recurring CEL for PO301.
    After some online checking, the shop eventually stumbled
    onto a few technicians that have run across these issues
    and cleaning the MAF is what solved the issue. And that's
    exactly what the shop's doing to fix mine.
    BTW, my K&N's been on for about 60,000 miles and I had
    just cleaned and reoiled it at around 50,000. That's when
    I started getting the CEL. I changed the plugs initially, thinking
    that was the problem.
    Right before leaving for a 300-mi TG trip, I disconnected the battery then pulled the MAF (easy!) and cleaned it with Brakleen (non-chlorinated) and reinstalled it. When I re-connected the battery and started the car the CEL was off and the car ran much better. Much of the hesitation(s) during WOT acceleration disappeared. During the trip (600-mo total) the CEL never came back on -BUT- I'm still sometimes having trouble with hesitations during acceleration or when the engine's otherwise under a load - like trying to maintain speed while climbing a long grade. It feels like a misfire to me, but as I said, no CEL has been thrown. RE: plugs, I just had the dealership do the 60,000-mi service and supposedly

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    Registered User AKESREX's Avatar
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    Hate having to figure this stuff out

    Yup. I feel for you. My dealership likes to play "I got a secret." What they told me to
    look at was plugs, coil packs and wiring. If I followed that regimen, I'd be miles away
    from where the problem actually was.
    I'll eventually learn this entire car, but it shouldn't be that way. Having had nothing
    but company provided cars (including this one) for the past 10 years, I can tell you
    that Subaru ain't exactly bowling me over with their support. (customer service or
    otherwise) They rank right up there with the worst I can imagine. Never bought a
    thing on my dime for a company car with either Ford or GM. I've had to strong-arm
    Subaru a couple of times on the WRX. Fortunately we're a vendor to them and I
    know the regional service rep.

  16. #15
    gfx
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    If you wanna clear a CEL, disconnecting the battery, pressing the brake pedal until the odometer disappears, then connecting it again can usually make it go away. I sometimes get a CEL in the cold cold weather, and that makes it go away.
    2003 5MT WRB WRX Sedan
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    http://www.cardomain.com/id/gfxwrx

    My car shots taken with my Canon 300D dSLR

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