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Thread: M40 Idle problems when summer and warm engin.

  1. #1
    Join Date
    Sep 2016
    Location
    Belgrade
    Posts
    145
    My Cars
    1989

    M40 Idle problems when summer and warm engin.

    Hello!

    I have BMW E30 with M40 swap from E34 seven years ago. When outer temperature low, everything is fine. But when is hot/summer I have idle problem after start up warm engine. Idle going under 500 rpm and engine has a tendency shutdown. I clean ICV, throttle, air flow sensor, check all hoses and vacum hoses. Also, sometimes when I push accelerator pedal one or two times, before start up warm engine, idle is fine.

    On what else to pay attention? Maybe on throttle valve switch? Injectors?

    Cheers,

    Elvir from Serbia/Belgrade.
    Last edited by Elvir; 06-21-2017 at 04:07 PM.

  2. #2
    Join Date
    Jul 2008
    Location
    Argentina
    Posts
    7
    My Cars
    1997 328i M E36 2D Hellrot
    Hello!
    I will tell you my experience. I have a 318i E30 with the m40 engine. I had idle problems specially once the engine was warm. Erratic idle speed and tendency to stall.
    My problem was the mass air flow sensor. I got a Chinese new maf from eBay and since then it's working perfect. No more idle problems or dropping rpm.
    I was surprised buy the build quality.
    But have in mind that there might be many different causes to idle problems.
    Good luck 👍

    Enviado desde mi SM-G955F mediante Tapatalk

  3. #3
    Join Date
    Sep 2016
    Location
    Belgrade
    Posts
    145
    My Cars
    1989
    Ok, thanks for the tip!

    What confuses me is that I do not have this problem when the winter.

    I'll see today behavior. Will be hot day.

    edit: Generaly, I always had "shaking" idle. Drive is fine. Nice and smooth.
    Some people told me, that problem of shaking idle maybe be bad seal on lower part of intake.
    Last edited by Elvir; 06-22-2017 at 03:55 AM.

  4. #4
    Join Date
    Sep 2016
    Location
    Belgrade
    Posts
    145
    My Cars
    1989
    Today, it is same problem. Weather is hot and idle going down. Then I turn off engine, I waited a little then turn on engine again and everything was ok.

    I will try with another MAF.

  5. #5
    Join Date
    Jul 2016
    Location
    Birmingham, UK
    Posts
    16
    My Cars
    92 E30 318i Convertible
    Sounds like it could be the MAF or an air leak somewhere in the intake that is causing the issue, try a MAF cleaner on the sensor to see if that works or WD40 on the pipes to see if it causes an RPM increase showing you where the leak could be.

  6. #6
    Join Date
    Sep 2016
    Location
    Belgrade
    Posts
    145
    My Cars
    1989
    Quote Originally Posted by MrGcc View Post
    Sounds like it could be the MAF or an air leak somewhere in the intake that is causing the issue, try a MAF cleaner on the sensor to see if that works or WD40 on the pipes to see if it causes an RPM increase showing you where the leak could be.
    Ok!

    I will check air leaks this weekend on intake, up and low part. Also, some people told me about fuel breathles valve and maybe he can make problem like this, special when warm.

    genuine-fuel-tank-breather-valve-13-90-1-711-395.jpg

  7. #7
    Join Date
    Sep 2016
    Location
    Belgrade
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    My Cars
    1989
    Ok, today is very hot day and there is no heavy idle drop.

    Also, I noticed that is vent hose cracked on down side. I use some tape for repairing and also use brake cleaner to clean hose. BTW, I ordered new hose! Inside of hose was a lot of black deposit.

    This is that hose, number 6.

    http://bmwfans.info/parts-catalog/E30-4-doors/Europe/318i-M40/L-M/feb1989/browse/engine/cylinder_head_cover/

    Also I use break cleaner to clean fuel breathles valve. In future I will check some another issues, because idle still a little shaking, but nothing to worry about for now.


    Last edited by Elvir; 06-24-2017 at 11:27 AM.

  8. #8
    Join Date
    Sep 2016
    Location
    Belgrade
    Posts
    145
    My Cars
    1989
    Hey guys, I think I've solved this problem.


    Definitely is a problem making by fuel breathles valve. When he stays in open position, petrol vapors flooded intake, when hot/summer time. Simply I remove valve and clean with brake cleaner.


    Since then, the idle is fine on very hot wheater this week.

  9. #9
    Join Date
    Apr 2020
    Location
    Romania
    Posts
    1
    My Cars
    BMW E30 318i
    Hello! Did you tear it down or did you clean only the pins on the outside?

  10. #10
    Join Date
    Mar 2021
    Location
    Santo Domingo
    Posts
    1
    My Cars
    1990 BMW 318i
    Hey, Linneo. I have a question, I also own an E30 318i with the M40 engine, what brand is the mass air flow sensor you bought? I bought a Kipa once and it only worked for a couple of weeks. I am currently having issues with my M40, my mechanic thinks it's the mass air flow sensor. If you can, please contact me asap, I'd love to hear from you since I'm having the same issues as you. Thank you.

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