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A clean mass airflow sensor seems to help

Discussion in 'Gen 2 Prius Fuel Economy' started by mfa-prius, Jan 20, 2010.

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  1. mfa-prius

    mfa-prius Old member

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    Over the last couple of years my mileage has been gradually decaying a couple of mpg, and the transition to/from ICE has been getting ragged. My dealer said the only thing they check for mileage concerns was the tire pressure, and suggested ethanol was to blame.

    Somewhere along the line I read that a dirty mass airflow sensor could cause both problems, so at yesterday's 65K oil change I also cleaned the MAF sensor. Preliminary indications are that this did the trick. MFD mileage is consistently and significantly better, and the rough ICE transition has disappeared. I'm not going to get too excited until after a couple of tanks of gas, but for now I'm cautiously optimistic.

    Cleaning only took a few minutes -- I removed the sensor and carefully scrubbed it with a soft toothbrush and isopropyl alcohol. It was obviously dirty, but not really grungy. No error codes on the computer that would normally indicate a MAF sensor problem.
     
    #1 mfa-prius, Jan 20, 2010
    offib, KK6PD, Toolman2009 and 3 others like this.
  2. ksstathead

    ksstathead Active Member

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    Rinse the toothbrush before bedtime!
     
    #2 ksstathead, Jan 20, 2010
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  3. andyprius

    andyprius Senior Member

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    Each time I check and clean the air filter I give the MAF sensor a hit with my spray cleaner. It takes about one second and is not necessary to remove it. There is a special spray cleaner for it and it's a worthwhile purchase. My mileage is consistently 50 mpg+
     
    #3 andyprius, Jan 20, 2010
  4. paprius4030

    paprius4030 My first Prius

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    What is the spray cleaner and where did you get it?
     
    #4 paprius4030, Jan 20, 2010
  5. mfa-prius

    mfa-prius Old member

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    ...or use a high-proof adult beverage, maybe?
     
    #5 mfa-prius, Jan 21, 2010
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  6. mfa-prius

    mfa-prius Old member

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    Apparently there's an official Toyota cleaner, but there's also a CRC and maybe other brands, available at most auto supply stores. I saw isopropyl alcohol recommended on the Web, and had some handy, so used it. I'll probably check out the MSDS for one of the commercial products, and see if I've already got the active ingredient(s) on hand, to avoid paying what is undoubtedly a huge markup for a common solvent.

    Also, removing the MAF sensor gives easier access to the throttle body and throttle plate, if you want to clean them at the same time (although there is, of course, yet another spray cleaner for that). You can probably tell I'm not a big fan of spray thingies.
     
    #6 mfa-prius, Jan 21, 2010
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  7. Patrick Wong

    Patrick Wong DIY Enthusiast

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    One diff between a MAF cleaner and a throttle body cleaner is that the former is supposed to clean without leaving any residue. The latter leaves a lubricating film. You definitely do not want to use throttle body cleaner on the MAF.

    mfa, how often do you change the engine air filter?
     
    #7 Patrick Wong, Jan 21, 2010
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  8. mfa-prius

    mfa-prius Old member

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    Interesting you should ask. My dealer replaced the engine air filter 2 times in 50K miles, as I religiously took it in every 5K miles. My maintenance guide, however, says 30K, 60K, etc. So I replaced it at 60K, and plan to watch it and replace every 30K miles unless it's really ugly. Seldom is there any sign of real grunge, in our clean Florida air. I've been tempted to vacuum it or blow it out with shop air at oil changes (10K, using synthetic), but that's generally discouraged, at least with aviation air filters.

    I'm also suspicious that the crud on the MAF sensor was put there by the same dealer when he cleaned the throttle body, since the mileage started to degrade at roughly the last time I had it serviced there.
     
    #8 mfa-prius, Jan 21, 2010
  9. SageBrush

    SageBrush Senior Member

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    Our Subaru was misbehaving for a couple of years: Full throttle would cause it to die, and even moderately taxing the engine with AC would lead to engine hiccoughs. The dealership thought it was a bad engine cylinder based on the codes they pulled, and recommended waiting for outright failure before embarking upon repair, since it was not clear what the problem was.

    Eventually the engine light prevented air pollution clearance, the MAF was replaced, and now all the problems we have had for years are gone.

    Just one more anecdote that the MAF can cause performance degradation way before a code is thrown that says "clean or replace MAF"
     
    #9 SageBrush, Jan 21, 2010
  10. andyprius

    andyprius Senior Member

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    The spray is CRC MAF Sensor cleaner, any auto store should carry it. The outside of the can promises a 4-10 HP gain to the wheels! (if you believe that) But the MAF sensor IS critical and should be cleaned regularly. If you do a search, PC discusses this in detail. PC= Priuschat
     
    #10 andyprius, Jan 22, 2010
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  11. tf4624

    tf4624 Active Member

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    Critical?LOL its pointless I bypass it and i tell what the computer needs to know..
     
    #11 tf4624, Feb 5, 2010
  12. mfa-prius

    mfa-prius Old member

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    That must keep you busy...
     
    #12 mfa-prius, Feb 5, 2010
  13. Genoz World

    Genoz World ZEN-style living

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    wow. that's great news. can you guys tell me the procedure of cleaning it? Do you clean both the MAS and throttle body? How is it done?

    thanks in advance.
     
    #13 Genoz World, Feb 5, 2010
  14. mfa-prius

    mfa-prius Old member

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    #14 mfa-prius, Feb 5, 2010
  15. jayman

    jayman Senior Member

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    I would NOT recommend "scrubbing" the MAF hot wires, they are very fragile and easy to damage. Using the CRC MAF cleaner, a 2-3 second burst from the can will leave the hot wires spotless

    For whatever reason, my FJ tends to leave heavy deposits on the MAF, and this is noticeable in lost fuel economy, lost performance, and the automatic begins to shift a bit erratically.

    So I get into the habit of cleaning the MAF every 3 months. Takes all of 3 minutes, and at this rate the CRC can should last me for years
     
    #15 jayman, Feb 5, 2010
  16. mfa-prius

    mfa-prius Old member

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    I probably shouldn't have said "scrub". I use a very soft toothbrush and almost no pressure. I also have a great dislike for aerosol sprays, so avoid them when there are alternatives.
     
    #16 mfa-prius, Feb 5, 2010
  17. priusevo

    priusevo Junior Member

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    This is exactly what I just did.I agree no need for removal.
     
    #17 priusevo, Oct 22, 2010
  18. PhazonPhobe

    PhazonPhobe His name is Sora

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    I'd be curious to try this. I've also been noticing a gradual drop in MPG on my '04. I'm fairly certain the battery isn't helping. I've noticed the lights will dim and windows get slow when I turn the car off.

    But definitely a helpful post. Thanks. ;p
     
    #18 PhazonPhobe, Oct 27, 2010
  19. PoutyPrius

    PoutyPrius New Member

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    I clean the MAF sensor and TBI myself, and my advice to you is make sure you hold on to the straw if you put the straw in the nozzle of the spray can when applying the throttle body cleaner to the plate. It saves a lot of money to do it yourself. But it saves a lot of time not having to fish the straw out of the air intake. I check the MAF sensor when I recharge the air filter and change the oil because it takes so little time. Just habit now. Good luck!
     
    #19 PoutyPrius, Nov 11, 2010
  20. eric29730

    eric29730 Junior Member

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    Where is the MAF sensor located?
     
    #20 eric29730, Nov 26, 2010
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