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Thread: Rough idle when cold

  1. #1
    Join Date
    May 2003
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    E36 M3, 2002

    Rough idle when cold

    I've got a 97 E36 M3 with about 160k (all mine). When I haven't driven the car for some time (more than several days between starts), the car will die while idling unless I stay on the gas pedal to keep the RPMs up. Once the car is warm, no issues.

    I've done plugs, cleaned out my ICV, and checked for any vacuum leaks (though I didn't smoke test so this was half-assed on my part).

    Any thoughts, ideas?

    Thank you

  2. #2
    Join Date
    Dec 2014
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    Guayaquil, Ecuador
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    1995 BMW 325i Sedan
    It’s curious. I happen to be having this issue, but when the engine is hot. This happens with more intensity with the shortest time I’ve has the engine off.


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  3. #3
    Join Date
    Jun 2010
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    NY
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    1997 328i
    Do you have ethanol in your gas year round? if not, add a bottle of dry gas. Or add a bottle of injector cleaner and drive it. Also clean your MAFS (especially if you have a air filter with oil on it).
    Attn. NEWBIES: Use the search feature, 98% has already been discussed.
    Click the search button, select "search single content type", select the "e36 sub forum" specifically, try the "search titles" then try the "search entire posts".

  4. #4
    Join Date
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    E34 525 1990 5HP18
    Unplug the coolant temperature sensor on the cylinder head. Then start again when cold. If the problem goes away you've found your culprit. If not plug it back in and unplug the mad and repeat. If that's not it then unplug the o2 sensor and repeat when cold. It's one of these.

    - - - Updated - - -

    Could also be two of these at the same time!

  5. #5
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    Quote Originally Posted by alang1990 View Post
    Unplug the coolant temperature sensor on the cylinder head. Then start again when cold. If the problem goes away you've found your culprit. If not plug it back in and unplug the mad and repeat. If that's not it then unplug the o2 sensor and repeat when cold. It's one of these.

    - - - Updated - - -

    Could also be two of these at the same time!
    Did you mean MAF, not mad? Unplug the connector? I’ll try these suggestions out thanks.

    I’m pretty sure the O2 s are original.




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  6. #6
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    Quote Originally Posted by Eric93se View Post
    Do you have ethanol in your gas year round? if not, add a bottle of dry gas. Or add a bottle of injector cleaner and drive it. Also clean your MAFS (especially if you have a air filter with oil on it).
    We do. E85. I only put premium gas in the car. Out here in Denver 91 is it. I should probably check the injectors 5 some point.


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  7. #7
    Join Date
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    Quote Originally Posted by djKibblez View Post
    Did you mean MAF, not mad? Unplug the connector? I’ll try these suggestions out thanks.

    I’m pretty sure the O2 s are original.




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    Yes maf. :-) Please follow my suggestions in sequence. And original o2 sensor ? New oem ones cost $30 shipped on amazon. If its a job you think you can do yourself, then replace it sometime in the next 6 months anyway.

  8. #8
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    Quote Originally Posted by alang1990 View Post
    Yes maf. :-) Please follow my suggestions in sequence. And original o2 sensor ? New oem ones cost $30 shipped on amazon. If its a job you think you can do yourself, then replace it sometime in the next 6 months anyway.
    I can’t reproduce the problem. Car idles cold just fine now. I don’t know if the ICV gets stuck intermittently when not used frequently. I disconnected the temp sensor and the maf separately and no change. Car idled fine. I’ll have to wait maybe a couple weeks to try again to see if the car dies.

    O2s are more than likely on their way out. I was just going to do the pre cats first since those are the more important ones but if they are only $30 on amazon I’ll give it a shot unless they are a cheap knockoff from China.

    Im fairly competent mechanically so replacing this or anything else is not an issue. It’s the troubleshooting I sometimes struggle with.




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  9. #9
    Join Date
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    You have 20 year old, 170k engine sensors. Bad idea. Since you are handy with a wrench, suggest you change the following out as soon as convenient :

    a. Engine coolant temp sensor
    b. Air temp sensor.

    Each costs $15-$20 shipped oem.

    c. Both O2 sensors. If you can't find it for $30-$35 shipped on Amazon for Bosch, check ebay.

    Unrelated to the engine issues :

    d. Radiator cap and bleed screw. $20 total oem.
    e. Fusible links x 2. Like $6 total.
    f. Fuel relay. $15

    All of the above should never be more than 100k. BMW did not make them to last that long. And most are fairly simple and quick to change out. Change them and the intermittent issues will probably just disappear or never appear. The engine's performance will also improve at least slightly. Prevention is the name of the game with these cars.

    No icvs do not typically get stuck after disuse for a few week as they are oiled by the ccv vapours, but that's one reason they get dirty over time. No harm removing it and your oil separator and cleaning both out with brakleen. Maf filament can be cleaned with the same spray too.

    Have you never changed your fuel filter ? Then please add that to the list $15 even if you don't have regular engine trouble. See chrisfix fuel filters on youtube for the vivid reason why.

    Good luck.

  10. #10
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    Thanks for those suggestion - yes I actually have several BMWs (2002, X5, E30) and they're normally kept up-to-date on maintenance but stuff just doesn't get driven and life gets in the way, blah blah, and boom, I'm here. Not a good excuse.

    I have cleaned out the ICV, MAF, replaced the ICV, cracked hose, plugs about 3 months ago. I have not done the fuel filter in quite some time...maybe several years.

    So I guess I've got a weekend of projects to work on! Thanks again. I'll report back at some point after all the maint is done.

  11. #11
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    I read the first post and my immediate thought was coolant temp sensor. I see nobody mentioned the battery as being a potential issue. I've seen my fair share of weird happening occur because of a low battery. Try putting it on a battery maintainer during the longer down times to see if the problem still arises.
    -Alex

  12. #12
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    Rough idle appears to be fixed, but the engine struggles to run when I first start the car and touch the throttle. The RPMS drop to the point where the car will die if I don't hold the throttle down and let the car warm up. Once the engine is warm all is well.

    I've replaced the following:

    ECT, air temp sensor, fuel filter, all O2 sensors, and cleaned the ICV (about 3 months ago).

    Spark plugs about 2k miles ago.

    Only other causes I can think of at this point are a vacuum leak.

    I'll try putting the batt on a tender to see if that makes a difference.
    Last edited by djKibblez; 11-22-2018 at 08:33 AM. Reason: New problem

  13. #13
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    Quote Originally Posted by djKibblez View Post
    Rough idle appears to be fixed, but the engine struggles to run when I first start the car and touch the throttle. The RPMS drop to the point where the car will die if I don't hold the throttle down and let the car warm up. Once the engine is warm all is well.

    I've replaced the following:

    ECT, air temp sensor, fuel filter, all O2 sensors, and cleaned the ICV (about 3 months ago).

    Spark plugs about 2k miles ago.

    Only other causes I can think of at this point are a vacuum leak.

    I'll try putting the batt on a tender to see if that makes a difference.


    My peake scanner is telling me something is up with the MAF. Is there a way to test to see if this is the culprit?


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  14. #14
    Join Date
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    I have been a frequent member of this forum for quite some time now, coming here asking for help, giving help and just about everyone here has been a wonderful resource and it really is a community. I have even met some of you in person at various CCA events.

    But every now and then there's someone that comes along who thinks they're better than everyone else.

    Thanks alang1990 for your help. Sorry I took the shortbus to school as a kid.



    douchebag.JPG
    Last edited by djKibblez; 11-24-2018 at 09:37 AM.

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