06-21-2022, 11:27 AM | #1 |
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Engine stumble on cold start
2015 M235i with 54k miles this just started a few weeks ago and only on overnight cold starts. I found some old threads from 2014 but no real resolution. Symptom only occurs on the very first start of the day. The car will start Rpms around 1200 to 1500 they will start to drop with a noticeable stumble sounds and feels like the engine is going to stall then the rpms pick back up. There are no codes of any kind being generated, the car runs completely normal no power loss or ruff idle after the first stumble. I am at a bit of a loss as to what it could be since anything I try will have to wait until the next morning to verify if it worked, spark plugs were done last year at the 40k mark no issues since then. I did clean the MAF sensor just as a starting point no change. Anyone have an issue like this that they where able to solve
Last edited by pmcmtnbkr; 06-28-2022 at 06:32 AM.. |
06-21-2022, 11:50 AM | #3 | |
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In a nutshell: On a warm engine that is turned off; unplug the MAF sensor. (while leaving the actual sensor in the intake pipe). Turn on the car, let it run for 10 full minutes (set a timer on your phone). Turn it off, plug back in the MAF. On the next cold start, it should be fixed. It seems over time the DME idle learning goes bad and this is a method to reset the idle parameters. yes exactly. |
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06-21-2022, 08:09 PM | #4 | |
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06-22-2022, 12:00 PM | #5 |
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This also happened to me last summer on my '16 and is documented with videos in a separate thread of mine. Exact same issue as yours, and my local Euro shop couldn't make any progress whatsoever. I wasn't fortunate enough to find the MAF process.
It eventually went away as the mornings turned cool and then cold, and didn't come back this year when they got warm again. Very strange. I'll also say my stock charge pipe just exploded a week ago and I'm in the middle of ordering a new one. With the charge pipe disconnected, my car starts but doesn't idle for long before completely conking out. Assuming too much air. In light of that issue, I had started to assume my issue last summer was maybe because the charge pipe connection was poor and was leaking air or something. |
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06-22-2022, 04:17 PM | #6 | |
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06-23-2022, 07:20 AM | #7 |
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+1 for the MAF fix. Finally fixed my stumble after unplugging it before a cold start. What's weird is that clearing the adaptions through BM3 didn't fix this. I figured that would be similar to the "hard reset".
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06-23-2022, 11:36 AM | #8 | ||
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Probably has to do with how BM3 adjust tables based on target boost as opposed to air volume and air temp like the factory table uses. |
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06-23-2022, 02:15 PM | #9 |
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Don't mean to hijack the thread, but it sounds like I should probably also do this MAF sensor reset procedure after getting the new charge pipe installed. I imagine my numbers will be all sorts of off, given that I drove about 30 miles with an exploded charge pipe. Atek would you agree?
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06-23-2022, 04:07 PM | #10 | |
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06-24-2022, 01:10 PM | #11 | ||
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06-24-2022, 01:42 PM | #12 |
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Well its up to you based on your goals/needs/desires. Do you like extra power and turbo noise?
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06-24-2022, 02:48 PM | #13 | |
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Is an intake upgrade one of these DIY, fairly inexpensive, low-hanging fruits that I should just do? |
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06-24-2022, 04:04 PM | #14 | |
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06-27-2022, 12:12 AM | #17 |
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06-27-2022, 06:09 AM | #18 |
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Which of these is the MAF sensor that I would need to remove for 10 minutes? I thought it was on the charge pipe, but I thought the tech at my shop told me it was on the intake. What's the name of each of these?
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06-27-2022, 08:10 AM | #19 |
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Ok, I'm going to answer my own question, but I'm happy to be corrected. The top box, located on the charge pipe, located closer to the throttle body, is the MAP (Manifold Absolute Pressure) sensor. The bottom box, located near the intake, is the MAF (Mass Air Flow) sensor.
The MAF sensor is the one we're talking about removing as part of the software reset procedure. I'm also considering cleaning it while it's out, though my tech said he recommends never cleaning them because it can leave behind residue and can fry them. How did I do? |
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06-27-2022, 09:24 AM | #20 | |
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06-27-2022, 08:26 PM | #21 | |
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06-28-2022, 07:00 AM | #22 |
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My car did this and still does occasionally. The MAF fix works every time I do it. But it usually comes back after significant changes in temperature day-to-day, and sometimes, I won't bother doing the reset and it'll go away and come back as it pleases. I wonder if a new MAF sensor will permanently resolve it, but I don't think I'll spend the money to find out.
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