04-01-2024, 11:30 PM | #1 |
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On Start Up-Rough Idle/Engine Shake
Hello everyone! I finally pulled the trigger and joined the forum! I have a 2018 M3 F80 with 56 miles. As far as mods I have VRSF catless downpipes, AA single midpipes with stick muffler that I TIG welded together, Mishimoto charge pipes, ER J pipe, NGK plug (gap .022), carbahn keyed crank hub, and bootmod stage 2 tune.
On a cold start (Note: I turned off cold start b/c no cats) my rpms will be stable for 2-3 seconds and then jump up and back down causing a very noticeable vibration to the engine. When it starts doing this I give it a little throttle and the rpms go back into range and the vibration stops. Now it doesn’t do this every cold start and very rarely it will do it after the engine is warm. I ran the DTCs and no codes. I replaced the spark plugs 5k miles ago, checked the ignition coils and cylinder 6 looked pretty toasted so I replaced it. Other than that everything looks good so what the heck is going on? I hope someone out there can help me out because I’m stumped! |
04-02-2024, 01:59 PM | #3 |
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Double check the tightness of the spark plugs. How new are the rest of the coils? I had a bad Bosch ignition coil on my N20 and it was causing rough idles and stutters through acceleration.
Also double check your chargepipe clamps and make sure everything is nice and tight. Any air leaks will cause the MAF sensor to tweak out.
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04-02-2024, 11:13 PM | #4 |
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theweebabySeamus383.50 |
04-02-2024, 11:43 PM | #5 | |
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04-03-2024, 02:23 AM | #6 |
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I had a similar issue on cold days with cold start disabled. The fix for me was to simply keep cold start enabled, even with catless downpipes!
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04-03-2024, 11:59 PM | #7 |
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Any luck on solving your issue?
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2014 BMW 328i xDrive - Black Sapphire - FBO Stage 2+ (SOLD) 1995 BMW M3 - Alpine White - 5MT Instagram: @boznien |
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04-06-2024, 09:54 PM | #8 |
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Hey xwilkinx thank you for your response. Yes, I did turn on the cold start and I’m still experiencing the issue. It actually didn’t make any difference which was kind of surprising.
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04-06-2024, 10:26 PM | #9 |
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Hey Boznien! No luck. I checked my charge pipes and j pipe and everything is nice and tight. I checked all my spark plugs and they’re all torqued to spec. I checked both coolant reservoirs and both are filled to the appropriate level. It’s strange that this only happens when I first start the car for the day. Today when I started it the engine had a significant rock back and forth. Enough to move the car side to side. No codes though! I have also notice a high pitch whining noise when I’m accelerating (it’s not turbos). It’s a much higher pitched sound and goes away after the engine is warmed up. This all started at the same time out of no where. Any help is greatly appreciated!
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04-08-2024, 06:34 PM | #11 |
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04-11-2024, 01:43 AM | #12 |
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Im sorry I do not. I’ve experienced it with other cars though. One time because I removed the screen on a cold air intake, which I mistakenly thought was there to stop any debris from getting through. When in fact, it was there to smooth the airflow before a curve in the pipe. Subsequently it disrupted the airflow to the mass airflow sensor and my idle started hunting. Put the screen back in and all was well again.
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04-17-2024, 07:23 PM | #13 | |
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04-28-2024, 03:11 PM | #15 |
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Ive changed all plugs+coils and that fixed the problem in my case. Got the same rough idle after cold start and i was unable to start driving without rpm drops or enginge off for the first 60 seconds.
My last set of coils held only ~6k miles |
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05-01-2024, 10:11 AM | #17 |
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Did you try flashing everything back to stock just to see if it keeps doing it? Sometimes it can be caused by the tune too I believe. I heard a couple of people experiencing weird stuff after having a tune for a while.
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