Subaru Idle Speed to Slow? Engine Turnning off When Coming to Stop

funnysht on 19/12/2020 - 10:26
Last edited 20/12/2020 - 15:18

Hi Everyone
Iv got a subaru forester 2011 manual and last 4 months iv noticed maybe 20% of the time when coming to a stop from 1st to neutral the engine stops.

I notice when this happens the rpm indicator goes low and then continues to go to zero with engine stopping. When it doesnt stop then i see the rpm going to low rpm and then automatically bounces up to prevent the engine turning off- which i assume is what its meant to do.

I though initially it may be a low idle speed but why does it happen only 20% of the time?
Any thoughts? Im planning on taking it to the mechanic next week but was hoping to get an idea about what the issue is and cost (i already replaced the spark plugs) cheers.

Update**
I did engine hard reset shown in link
https://www.youtube.com/watch?v=Ud6OU13IDSQ&feature=emb_logo

Seems to be idling more smoothly and touch wood has not stalled. So thanks! If it doesnt wlrk il just clean the MAF👍😁

Automotive Car Subaru SUV

Comments

  • Muzeeb on 19/12/2020 - 10:30

    Are you using the clutch correctly?

    • funnysht on 19/12/2020 - 10:34
      +1

      Had car 5 yrs so yes. Never had this issue before . Being driving manual for 15 yrs
      Plus i think it is the response to low rpm speed. I think sometimes the car doesnt detect low rpm. I mean for example i just put on neutral i can see the rpm slowwing down all the way to zero 20% of the time causing the engine to turn off. It shouldnt do that- normally it bounces back automatically to higher rpm

  • Darayus on 19/12/2020 - 10:43
    +3

    hi,

    Get your car upper engine clean up as well as throttle clean up, this will allow the air to pass through freely and allow the engine to run without stalling. Also try to use the Engine fuel injector cleaner in your fuel system every 5K drive this will assist you to clear up any junk build up on fuel injector head.

    Dont know what fuel you use, try using 98 Octane fuel atleast 2 to 3 tank and see.

  • funnysht on 19/12/2020 - 10:47

    I use octacne 98 usually.
    But i guess i see the rpm indicator going all the way to zero when neutral sometimes. Does a throttle clean up help..i thought it may be a problem with the the engine noy detecting low rpm

    • pjetson on 19/12/2020 - 19:40
      +2

      i see the rpm indicator going all the way to zero when neutral sometimes

      I think you're seeing the result of a problem, not the cause of the problem.

      • funnysht on 20/12/2020 - 01:29

        that explains a lot thatnk!

  • pao2x on 19/12/2020 - 11:38

    Used to adjust these manually in carburetor cars. I don't know about ECU FI cars. My first guess is bad fuel or needs a new fuel filter (clogged up and fuel line pressure drops)

  • yayrobots on 19/12/2020 - 11:40

    Had something similar in my car where it would almost stall (rpms would bounce up and down at idle) but it also had reduced power output and a slight fuel smell when rev'd in neutral. The issue was a lean condition due to an air intake leak after the air flow sensor but given the age of your car it would more likely be a bad sensor.

  • apsilon on 19/12/2020 - 11:50
    +5

    This is very common on Subarus, it's a dirty throttle body essentially causing the butterfly to stick so the car can't adjust quickly enough. Symptoms will start with RPMs dipping as you come to a stop and as it gets worse the car will eventually start stalling. Normal service procedure includes the use of upper cylinder cleaner passed through the throttle body but if you're getting the car serviced by a non Subaru mechanic or not servicing it at all this is often skipped. Easy enough to remove and clean though you'll probably need to replace the gasket. Plenty of Youtube videos covering the issue and cleaning process.

    • funnysht on 20/12/2020 - 01:32

      cool that perfectly explains it.

  • spychiatrist on 19/12/2020 - 12:03
    +3

    MAF sensor. Ex-Liberty owner here.

    • funnysht on 19/12/2020 - 20:55

      is MAF sensor a do it yourself job? or how much it would cost?

      • neo on 21/12/2020 - 09:53

        Super easy to clean. It's a small electronic component just after the air filter. You'll see it screwed onto the intake. You take it out and spray with MAF sensor spray or electronics spray.

  • t_c on 19/12/2020 - 12:03
    +2

    I purchased a vehicle at auction that had rough idle and a engine light on. I bought a scan tool on ebay which showed bad o2 sensor, so I replaced both for $30 each. all fixed.

  • Cheeper on 19/12/2020 - 13:05

    Clean your MAF sensor and throttle body and go from there.
    How many km's on it ?

  • bhubb18 on 19/12/2020 - 19:47
    +1

    MAF
    IACV blocked / sticky
    Vacuum leak

    Start off with checking them, and see how you go :)

    • funnysht on 19/12/2020 - 20:55

      is MAF sensor a do it yourself job? or how much it would cost?

      • bhubb18 on 19/12/2020 - 23:55
        +1

        Very easy to DIY.

        Try using a MAF / AFM cleaner on it before replacing though, because they're not particularly cheap.

        • funnysht on 20/12/2020 - 01:28

          thanks i looked on youtube looks easy- do i need to disconnect the battery before doing it?

          • bhubb18 on 20/12/2020 - 09:34

            @funnysht: Not really necessary, but if you want to be extra safe, sure.
            Disconnecting the battery will also allow the ECU to relearn idle levels etc too, after a bit of a drive.

    • apsilon on 20/12/2020 - 06:17

      They don't have an IACV, that function is achieved via the throttle which is why once it starts sticking the vehicle starts stalling. Could be the MAF but dirty sticking throttle is a common problem on Subarus with an electric throttle so definitely the number one suspect.

      • bhubb18 on 20/12/2020 - 09:36

        Ah fair enough, I'm pretty sure my old outback did have one but that was before electronic throttle control anyway haha

  • stainedteatowel on 19/12/2020 - 22:47

    Few others have mentioned it already, try cleaning the throttle body. Caused my mazda 3 to stall at idle

  • shaneiwey on 20/12/2020 - 09:54

    I had the same problem on my 2004 forester. As another commenter said it was the IAC Valve. Spent ages trying to find a 2nd hand replacement (new one is 500 fkn dollars). Ended up being able to disassemble my one and clean the shit out of it. Still working a year and a half later. Upper engine cleaner should help too. Not sure if relevant to your foz tho.

  • OzHunterNSW on 20/12/2020 - 10:18

    The magic of……WD40….

    What do you think?….. I bet you think the vehicle is a full on 4x4, so I am assuming you drive on dirt.

    Maybe things are a bit dusty under the hood…. don't you think?

    I suggest spraying WD40 upon all mechanical linkages to clean, free-up, and lubricate.

    Don't you think this would be a good idea?

    • funnysht on 20/12/2020 - 11:02

      dont think thats the problem mate

  • funnysht on 20/12/2020 - 11:03

    Thanks everyone i have done this first if anyone else has similar problems:

    https://www.youtube.com/watch?v=Ud6OU13IDSQ&feature=emb_logo

    Then i will try cleaning th MAF sensor if still not working

    Then 3rd would be clean the throttle body

    4th…swap cars with the wife

    • apsilon on 20/12/2020 - 11:54

      Then i will try cleaning th MAF sensor if still not working

      Be careful if you decide to do this as they are somewhat fragile. Don't scrub/poke it. If it were the MAF you'd almost certainly have symptoms other than when coming to a stop as it operates at most throttle positions but your issue is only at zero throttle. It's not impossible but it's also not likely IMO.

  • whitelie on 20/12/2020 - 12:07

    This is the stuff you want. The genuine Subi one is the best, don't bother with the Nulon equivalent…can probably get it slightly cheaper thru eBay

    • apsilon on 20/12/2020 - 15:02

      That's the right stuff for regular maintenance but once it gets to the point that it's stalling, it's easier, faster and cheaper to pull and clean off the vehicle than pump can after can (at ~$20 a pop) of that through hoping it works.

  • HeWhoKnows on 20/12/2020 - 15:34

    Please Dont try and guess the answer!
    The advice given here is very good but also general in nature that wont necessarily solve your problem.
    I had the same problem on a Mitsubishi Lancer manual vehicle.
    Turned out the car needed a new idle speed motor. Its a fairly simple fix but the price of the part could be the costly part.
    So that could also be your problem though on yours it could be the idle air control valve.
    Take it to a mechanic or auto electrician to get it diagnosed properly or you might find yourt self stuck someone unable to drive the car!

    Meanwhile you might find this post useful:
    https://www.yourmechanic.com/estimates/subaru/forester/when-…

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