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      03-15-2015, 05:09 PM   #1
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Drives: 2012 135i DCT
Join Date: Apr 2014
Location: Maryland

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N55 Idle Fluctuation/Surge + Codes

Sorry for a long post.

2012 N55 DCT
FBO + Cobb Stage 2+
DME updated to latest integration level.

Yesterday out of nowhere I experienced a problem with low idling and surging when coming to a stop. Basically it was as if my car was about to stall every time I started coming to a stop, it would drop to about 400 and then surge to 1200 while I was braking, which would cause the car to try and lurch forward. It never stalled, but the idle was not normal and I got some codes. Here are the first 2.

Rail pressure sensor, plausibility: Maximum pressure exceeded
The diagnostic function monitors the fuel rail for excessive pressure levels prior to the engine start.

Mixture adaptation, lower engine speed range: Mixture at partial load too lean
System Too Lean (Bank 1)

So I cleared the codes and went for another drive. Experienced the same behavior and got this code.

Fuel supply system, oxygen sensor emissions control: upper limit exceeded

The diagnostic function monitors the lambda closed-loop mixture control. The mixture is too lean and the lambda control enriches it.

Uninstalled the Cobb this morning and put 7.5 gallons of 93 oct (Which I always use) and all of the symptoms seem to be gone. No codes. Any idea what this could mean? I'm worried because I'll be installing the Pure Stage 1 upgrade soon and I don't want any fueling issues to arise.

Thanks in advance.
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      06-16-2018, 11:18 AM   #2
YearOneOne's Avatar

Drives: 13 135i mineral grey
Join Date: Jun 2016
Location: Maryland

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Did you ever figure out what this was as I am experiencing the same symptoms
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      06-25-2018, 12:18 PM   #3
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Drives: Carbon Black 2013 135is
Join Date: Feb 2018
Location: Palm Beach County, FL

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Did you ever get your DME updated?

SIB 12 15 14 was put out to address the idle surge issues when coming to a stop.

See this threads:

My 2013 135is DCT was having the same issues, which were exacerbated by the AC being on.

The idle would always drop to about 500 RPM, then surge up over 1k, then settle down at 700RPM.

To add to this i was having bad throttle delay/lag occasionally where the car wouldn't do shit when i was pulling into traffic which is very dangerous.

I got the update about a week ago, my car is out of factory warranty so it was 2 hours of labor which my extended warranty covered thankfully.

The throttle delay appears fixed, there is still a little idle surge but its not nearly as bad as it was previously. HOWEVER, i will say that the loud burbles and pops that came with my PPK and Performance exhaust are gone, the burbles and pops are very muffled after the update. Im hoping my PPK wasnt erased in the process of updating the DME, the SA said it wouldn't but im waiting for another knowledgeable person to chime in. I miss my burbles and pops.
2013 Carbon Black 135is (n55) #166

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