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      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; Yesterday at 06:32 AM..
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      06-21-2022, 11:48 AM   #2
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Wow just did another search for this and found a ton more post oops must have been the way I phrased my search
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      06-21-2022, 11:50 AM   #3
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Quote:
Originally Posted by pmcmtnbkr View Post
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 rims 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
So I had this issue, and read through all the threads on this forum and others for the matter. (quite a bit info on here but it is a lot of reading through posts)

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.



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Originally Posted by pmcmtnbkr View Post
Wow just did another search for this and found a ton more post oops must have been the way I phrased my search
yes exactly.
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      06-21-2022, 08:09 PM   #4
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Quote:
Originally Posted by atek View Post
So I had this issue, and read through all the threads on this forum and others for the matter. (quite a bit info on here but it is a lot of reading through posts)

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.
thanks for the information I have given it a try and will see what tomorrow morning brings. I can say after doing this and clearing the codes the cars engine idle is even smoother now than it was. I have read through so many post tonight and many had the same thought process it normal, its HPFP, and replace a bunch of parts. Only 1 or 2 made any mention of the MAF sensor and your information is by far the best and most logical process thank you
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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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Quote:
Originally Posted by MegaMatt3 View Post
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.
I found your videos and that is exactly how mine is acting I already have replaced the charge pipe a few months ago. What I find interesting is i never had a problem for the 2.5 years I have owned the car until just a few weeks ago. I would recommend doing what is outlined above even if your symptom resolved I have definitely noticed a big difference in how the car is running
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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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Quote:
Originally Posted by pmcmtnbkr View Post
thanks for the information I have given it a try and will see what tomorrow morning brings. I can say after doing this and clearing the codes the cars engine idle is even smoother now than it was. I have read through so many post tonight and many had the same thought process it normal, its HPFP, and replace a bunch of parts. Only 1 or 2 made any mention of the MAF sensor and your information is by far the best and most logical process thank you
I can't take all the credit, was posted by another veteran member on here but the thread is pretty old. Glad you were able to notice the smoother idle right away, I sure did as well. I'm going on day 4 (did this Sunday evening) since doing this fix and the car starts great every cold start!
Quote:
Originally Posted by MegaMatt3 View Post
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.
The reason it won't idle long before stalling out is because it doesn't have accurate readings from the MAP sensor (the sensor on he chargepipe closest to the throttlebody). So the DME is seeing air volume from the MAF that doesn't match up with what the MAP sensor is seeing = DME freaks out and throws too much or not enough fuel = stall out. Best to not run the car until you can get the charge pipe fixed.

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Originally Posted by 1more1 View Post
+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".
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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Quote:
Originally Posted by MegaMatt3 View Post
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?
Definitely wouldn't hurt, do you also plan on doing aftermarket intake or staying stock?
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      06-24-2022, 01:10 PM   #11
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Quote:
Originally Posted by atek View Post
Quote:
Originally Posted by MegaMatt3 View Post
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?
Definitely wouldn't hurt, do you also plan on doing aftermarket intake or staying stock?
Had not planned on an aftermarket intake, but I have basically no experience doing aftermarket upgrades, so I'll rely on you and the other fine folks here to tell me I should.
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      06-24-2022, 01:42 PM   #12
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Had not planned on an aftermarket intake, but I have basically no experience doing aftermarket upgrades, so I'll rely on you and the other fine folks here to tell me I should.
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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Quote:
Originally Posted by atek View Post
Quote:
Originally Posted by MegaMatt3 View Post
Had not planned on an aftermarket intake, but I have basically no experience doing aftermarket upgrades, so I'll rely on you and the other fine folks here to tell me I should.
Well its up to you based on your goals/needs/desires. Do you like extra power and turbo noise?
Lol. I like extra power, yes. Turbo noise doesnt bother me. I'll admit, based on your advice in my charge pipe thread, I'm considering a Dinan or BMS tune but haven't gotten far in my research.

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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Originally Posted by MegaMatt3 View Post
Lol. I like extra power, yes. Turbo noise doesnt bother me. I'll admit, based on your advice in my charge pipe thread, I'm considering a Dinan or BMS tune but haven't gotten far in my research.

Is an intake upgrade one of these DIY, fairly inexpensive, low-hanging fruits that I should just do?
Yes, and Yes.
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      06-25-2022, 07:35 AM   #15
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Well I think this has worked the past few cold starts have been issue free
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      06-25-2022, 08:27 PM   #16
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Well I think this has worked the past few cold starts have been issue free
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      06-27-2022, 12:12 AM   #17
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Well I think this has worked the past few cold starts have been issue free
Its been a solid 7 days with 2 daily cold starts for me and no issues!
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      06-27-2022, 06:09 AM   #18
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Quote:
Originally Posted by atek View Post
Quote:
Originally Posted by pmcmtnbkr View Post
Well I think this has worked the past few cold starts have been issue free
Its been a solid 7 days with 2 daily cold starts for me and no issues!
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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Quote:
Originally Posted by MegaMatt3 View Post
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?
Got the locations right but don't take the MAF out, just unplug it.
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      06-27-2022, 08:26 PM   #21
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Quote:
Originally Posted by MegaMatt3 View Post
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?
Correct, the MAF is the lower sensor directly on the intake. You can clean MAF safely you just have to use specific MAF CLEANER that can be bought at local auto parts store. It says MASS AIR FLOW / MAF CLEANER on the bottle, usually next to brake clean- though they ARE NOT INTERCHANGEABLE. Make sure you get MAF cleaner. And do NOT use anything to wipe it. The pressure from the can is enough, no rags or towels or q-tips necessary.
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      Yesterday, 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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