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Thread: 525I Rough idle and loss of power issue

  1. #1
    Join Date
    Jan 2016
    Location
    Chatfield, MN
    Posts
    3
    My Cars
    1995 BMW 525I

    525I Rough idle and loss of power issue

    Hi everyone,

    Newbie here.....

    I have been having issues with my 525I recently with rough surging idles when warm and a low RPM power problem. When I start the car is start fine and idles normally. After warming up a few minutes the idle become ruff and irregular. It does not stall but hesitates on rev and smooths out when RPM gets near 2500 RPM. When driving it will drive normal on highway driving but when requiring more power it will jerk a bit and have like a bad timing feel. It will also surge in and out of that and a normal power feel. Was getting 25 mpg mixed highway and city. lately 24.5. (averaged so it might be a bit worse). looked for vacuum leaks with no success. No obvious noises. Coils and plugs looked normal.

    Any ideas?

    Thanks,

  2. #2
    Join Date
    Jul 2011
    Location
    Arlington, VA
    Posts
    9,933
    My Cars
    2018 BMW M240i
    Have the intake system smoke tested. A visual inspection won't find leaks. Also, have the codes read. That's always the first step. Post the codes so we can help you.

    The reason why the engine idles fine for a couple of minutes is because the engine is in the "open loop" mode. The engine computer (ECU) ignores the data from the O2 sensors and runs the engine on a rich fuel/air mixture. It does this to get the cats up to temperature quickly. Once the coolant reaches a specific temperature, the ECU reverts to the "closed loop" mode, which is the normal mode of operation.
    Last edited by MarcoZandrini; 01-22-2016 at 08:37 AM.

  3. #3
    Join Date
    Jan 2016
    Location
    Chatfield, MN
    Posts
    3
    My Cars
    1995 BMW 525I
    Thanks for the advice Marco. I will check that out. Will have the car scanned and see about the smoke test.

    Thanks

  4. #4
    Join Date
    Jan 2016
    Location
    Chatfield, MN
    Posts
    3
    My Cars
    1995 BMW 525I
    Just checking back in about this issue. I was loosing my coils one at a time. I replaced a few to test and then finished with all of them. What a difference. Tons of power ( well as much as the engine could provide) and huge gain in gas mileage.

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