2011 BMW 325i rough idle on first start

Discussion in '3 Series' started by Gary, Jun 29, 2020.

  1. Gary
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    Gary

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    I have a 2011 325i with 64000 miles on the clock. Over the last week or so it has developed a rough idle where I can feel the car judder slightly and the rev needle bounces up and down slightly, then when I accelerate away I can feel a misfire and slight judder. But after 5 minutes of driving it settles down and runs smoothly. If I turn the car off and on again after its been running it will be fine unless I leave it for a good few hours. It has full BMW service history but is overdue by about 2000 miles. I have got it booked in for a service with BMW in 2 weeks time. I thought it might have been injectors, spark plugs, MAF sensor, coil packs or something bbut don't understand why the problem goes away after 5 minutes when the car is warm.


    Has anyone got any ideas what this problem could be before I start throwing money at it.


    Thanks, Gaz
     
  2. snrbrtsn
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    snrbrtsn WARLORD Site Supporter

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    There’s likely tens of reasons so it would make remote diagnostics difficult and/or expensive with a game of Russian roulette style trial and error
    Best having codes read, from description:

    “If I turn the car off and on again after its been running it will be fine unless I leave it for a good few hours.”


    I’d suggest HPFP however, it could equally be a bad coil pack, without reading fault codes I’d be playing the guessing game
     
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  3. Wynne71
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    Wynne71 Site Supporter

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    Hello Gaz.

    I had a 2008 325i with the same N53 engine, loved the silky smooth power and the upper end growl.
    Had a very, very similar issue with the car, at first start it would idle erratically, I could watch the needle wave up/down slightly. There was also a slight cough when taking off, both of these went when the car was warm.
    I had the codes read and it came up as a bad coil pack. Bought a new one, no change at all.
    I remember putting the supposed bad coil in each cylinder at a time to see if I could get the car to replicate on different cylinders. It wouldn’t.
    This went on for a month or so, was around the time the car was due to be replaced, so I moved it on and bought an F30.
    Sorry but I can’t give you the answer! I’d go with the advice of getting the codes read, even if no error light (no CEL or errors on mine) it will store the misfire etc.

    Good luck.
     
  4. Gary
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    Gary

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    Thanks for your reply.

    Thanks for your reply, I will take it and get the codes read. I'll get them done at BMW while it's being serviced.
     
  5. slim_boy_fat
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    slim_boy_fat WARLORD Site Supporter

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    Welcome aboard, Gary. :wavey: As the lads have said, codes will be your friend, but it could be a cam or crank sensor causing the problem. You're right in not throwing cash at her in the hope of hitting the problem, that way lies sorrow....well, the possibility of unnecessary expense. :(

    Keep us updated with your findings.
     
  6. kleynie
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    kleynie WARLORD Site Supporter

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    I’d put money on the NOx sensor, especially if it’s bad on mpg? It could also be HPFP as mentioned already, injectors, coil packs etc, etc. I had a 525 with the same N53 engine, I had all the above replaced before it ran properly, and it was only on 30 odd thousand miles at the time.
    Also worth checking that the fuel filter has been replaced, it’s often overlooked.
     
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  7. a.s.uk
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    a.s.uk

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    Sensor at the rear of the exhaust that’s always rusted in was my bosses problem with his car
    Was a complete tw@t to change but was ok after that
    Is it the Nox sensor I think?
    Same age to yours


    Sent from my iPhone using Tapatalk
     
  8. kleynie
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    kleynie WARLORD Site Supporter

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    Yep, that’s the NOx sensor, they are not cheap.
     
  9. Wynne71
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    Just to add to this, I searched through my old YouTube clips as I remembered recording the issue with mine.
    Originally it was a rough idle when cold, this then moved onto a weird set of circumstances where it would switch to erratic idle with the clutch down and in gear, but not when in neutral. Had forgotten this part!
    Obviously more than a simple coil pack.

    Here’s the video I took:




    Didn’t get to the bottom of it I’m afraid.
     
  10. snrbrtsn
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    snrbrtsn WARLORD Site Supporter

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    To throw another theory.
    It could be a carbon coked inlet manifold, the realms of possibility remain abundant without reading the car it’s can turn into an expensive guessing when in fact in could simply be a cracked/perished £3 vac pipe......
     
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