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      07-27-2021, 09:06 AM   #20
Silverlining_m2
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Drives: 2023 M2, 2024 m235i
Join Date: Mar 2020
Location: Michigan

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Going back to stock intakes should always be an early or first step in diagnosing rough idle.
I had rough idle when going to flex fuel. This is what I had to do (it took me darn weeks of troubleshooting):

- Removed aftermarket intakes
- Installed OEM intake with paper filter
- Clean MAF sensor
- Swapped new maf sensor
- Fixed some wiring issues on flex fuel related to the ethanol sensor
- Changed to flex fuel plugs and adjusted gap to .020 per Cary Jordan
- Disabled cold start
- Disabled start up roar

When I disabled start up roar, my idling issue went away. Seems like start up roar gets confused with ethanol mixes and caused my choppy idle.
Interestingly enough, I had rough idle on cold start, and it was alleviated by removing the start up roar as well. My car is stock, with bm3 stage 1.
Do you have aftermarket intakes? If so, which ones?
Nope. My car is all the way stock aside from the the flash tune and some pretty stuff.
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2023 M2. ZB. Manual.
2024 m235i
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