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2Addicts | BMW 2-Series forum Technical Topics N55 (M235i) Engine, Transmission, Exhaust, Tuning m235i lean code running rough at idle

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      01-29-2023, 10:58 PM   #1
Rainy_Days
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m235i lean code running rough at idle

Hey everyone my f22 is running rough at idle and is throwing the mixture too lean code. I read a few forums but seems like mileage varies for the issue. Question is more about the mixture too lean since most forum replies seem to say rough idle when it's cold is common.
Get the mixture too lean code on both a 91 and E30 Tune. Thanks!

Running BM3 on the OTS E30 Tune
Dinan Intake
CRSF Intercooler
VRSF Catless DP
FTP Charge Pipe
FTP Turbo Inlet
NGK Plugs

Here's a Data Log at WOT in Sport https://www.bootmod3.net/log?id=63d6...90c6a80c853c56
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      01-30-2023, 07:43 AM   #2
designatedposter
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turn on LTFT. if you have a vacuum leak, it will show as positive fuel trim e.g. 1.15
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      02-26-2023, 07:33 PM   #3
Toomuchboost
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I fought a similar issue this summer. Found 2 issues, my downpipe to midpipe gasket had failed causing a small exhaust leak and my primary oxygen sensor had failed without throwing a check engine light. Replaced gasket and clamp and installed new oem upstream oxygen sensor and haven't had an issue since. I did find lots of threads and info regarding possible causes, ideally a boost/smoke check should be performed to confirm that there aren't any failed seals/leaks causing your lean condition. Check your pcv breather tube very gingerly as they tend to break by merely breathing on them.
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      02-27-2023, 08:45 AM   #4
designatedposter
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downpipe to midpipe gasket is after all o2 sensors, i would think it should not have any impact on fuel trim.

a failed upstream o2 sensor is critical though. how did you diagnose this?
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      03-03-2023, 11:05 PM   #5
atek
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check for boost/vacuum leaks
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