Normal for N54 w/6MT to miss at idle?

jeffro535 · 09-11-2013, 06:44 PM

Car otherwise runs fine, it's been in the dealer (a lot) under both full and CPO warranty for all the usual N54-isms (turbos, hpfp, vanos solenoids) but it always has done this lean misfire thing when it's warm outside and the AC is off. The Tech Service Engineer rode with me and said that it this was normal behavior with a manual transmission. He elaborated that the DME is always looking for the leanest point the engine will run at and will take the mixture "to the very edge of lean misfire" and it was just the DME doing its lambda cycle. My counterpoint was that it was indeed lean misfiring, not just going to the edge, therefore something was wrong (slow O2 sensor?) He replied that without a load on the motor it was totally normal for it to do that and not to worry about it. If it sits long enough it will indeed settle down after awhile, but I've never driven a BMW that did something like this. So the question that I have to the other folks that have a N54 with a 6MT is does yours do the same thing or do I no kidding have a problem and they don't want to deal with it.
Thanks in advance

ThEnder · 09-11-2013, 06:50 PM

I get an occasional idle misfire but usually when the engine is cold. Also N54 6MT

blacknbean · 09-11-2013, 07:12 PM

very slight miss every once in a while that makes it shake a bit when cold. warm is pretty stable. MUCH less after cleaning carbon from intake valves.

Blackhawk36 · 09-11-2013, 07:59 PM

Smooth as silk all the time.

T1M · 10-25-2015, 05:51 AM

I know it's an old post but I just bought a 1M and I have this exact phenomenon too. Runs fine under full boost, no breakup, never skips a beat when cruising or holding a given rpm when stationary. When left to idle on its own it's solid and stable, rpm does not move, it's a purely audible miss that happens every 30 - 60sec. I went searching online and found this post. Doesn't concern me if it's normal lean misfire but odd it's not targeting 14.7 afr at idle - to lean misfire it'd have to be upwards of 16-17:1 afr... Anyone else got something to add to this?

GMWNashville · 10-25-2015, 08:03 AM

Usually I've seen this caused by carbon buildup..while the car runs leaner at idle it still should not misfire.

Fundguy1 · 10-25-2015, 08:14 AM

Quote:

Originally Posted by Blackhawk36

Smooth as silk all the time.

+1. 223,000 miles worth.

John 070 · 10-25-2015, 08:46 AM

I would say not normal....6mt....

Dann · 10-25-2015, 10:17 AM

Mine has a small cough every now and again but it's done nearly 60k without a walnut blast.
I think mine is down to that

T1M · 10-25-2015, 11:10 AM

Hmm mine has only done 35,700 kms (22,183 miles). For carbon build up to cause a misfire only at idle it would have to be really significant, to the point where normal airflow is that disrupted/blocked that normal combustion doesn't occur. That seems extreme to me, given it's fine at all other times.

I mean if I watch the rpm at idle it's solid. Feels smooth when cold and warm. It's just an occasional audible miss, can happen once every 30-60sec, then nothing for a couple mins then once then nothing for a few more mins. It's erratic, but it does happen. No misfire codes occur. I should log it with a wideband to see what the idle afr is.

09-11-2013, 06:44 PM	#1
jeffro535 First Lieutenant 16 Rep 311 Posts Drives: 2020 M340i, 2019 X3M40 Join Date: Feb 2012 Location: SoCal iTrader: (0)	Normal for N54 w/6MT to miss at idle? Car otherwise runs fine, it's been in the dealer (a lot) under both full and CPO warranty for all the usual N54-isms (turbos, hpfp, vanos solenoids) but it always has done this lean misfire thing when it's warm outside and the AC is off. The Tech Service Engineer rode with me and said that it this was normal behavior with a manual transmission. He elaborated that the DME is always looking for the leanest point the engine will run at and will take the mixture "to the very edge of lean misfire" and it was just the DME doing its lambda cycle. My counterpoint was that it was indeed lean misfiring, not just going to the edge, therefore something was wrong (slow O2 sensor?) He replied that without a load on the motor it was totally normal for it to do that and not to worry about it. If it sits long enough it will indeed settle down after awhile, but I've never driven a BMW that did something like this. So the question that I have to the other folks that have a N54 with a 6MT is does yours do the same thing or do I no kidding have a problem and they don't want to deal with it. Thanks in advance
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09-11-2013, 06:50 PM	#2
ThEnder First Lieutenant 26 Rep 336 Posts Drives: E90 LCI N54 6MT Join Date: May 2013 Location: San Francisco iTrader: (0)	I get an occasional idle misfire but usually when the engine is cold. Also N54 6MT
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09-11-2013, 07:12 PM	#3
blacknbean Major 14 Rep 1,044 Posts Drives: e92 335i 6MT Join Date: Jul 2007 Location: LA iTrader: (2)	very slight miss every once in a while that makes it shake a bit when cold. warm is pretty stable. MUCH less after cleaning carbon from intake valves.
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09-11-2013, 07:59 PM	#4
Blackhawk36 Captain 30 Rep 644 Posts Drives: 2007 335i 6MT No iDrive Join Date: May 2009 Location: MD iTrader: (0)	Smooth as silk all the time.
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10-25-2015, 05:51 AM	#5
T1M Captain 196 Rep 657 Posts Drives: AW MY12 1M Join Date: Jun 2015 Location: Melbourne, Australia iTrader: (0)	I know it's an old post but I just bought a 1M and I have this exact phenomenon too. Runs fine under full boost, no breakup, never skips a beat when cruising or holding a given rpm when stationary. When left to idle on its own it's solid and stable, rpm does not move, it's a purely audible miss that happens every 30 - 60sec. I went searching online and found this post. Doesn't concern me if it's normal lean misfire but odd it's not targeting 14.7 afr at idle - to lean misfire it'd have to be upwards of 16-17:1 afr... Anyone else got something to add to this?
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10-25-2015, 08:03 AM	#6
GMWNashville Colonel 172 Rep 2,373 Posts Drives: 19 G05, 16 F80, 10 E70x5D Join Date: Jan 2008 Location: Nashville, TN iTrader: (2)	Usually I've seen this caused by carbon buildup..while the car runs leaner at idle it still should not misfire.
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10-25-2015, 08:46 AM	#8
John 070 Lieutenant General 1705 Rep 14,829 Posts Drives: 335i cpe Join Date: Oct 2006 Location: ZSP/ZPP/ZCW iTrader: (0)	I would say not normal....6mt....
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10-25-2015, 10:17 AM	#9
Dann Major 132 Rep 1,381 Posts Drives: E90 LCi 335i Join Date: Feb 2015 Location: Portsmouth, United Kingdom iTrader: (0)	Mine has a small cough every now and again but it's done nearly 60k without a walnut blast. I think mine is down to that
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10-25-2015, 11:10 AM	#10
T1M Captain 196 Rep 657 Posts Drives: AW MY12 1M Join Date: Jun 2015 Location: Melbourne, Australia iTrader: (0)	Hmm mine has only done 35,700 kms (22,183 miles). For carbon build up to cause a misfire only at idle it would have to be really significant, to the point where normal airflow is that disrupted/blocked that normal combustion doesn't occur. That seems extreme to me, given it's fine at all other times. I mean if I watch the rpm at idle it's solid. Feels smooth when cold and warm. It's just an occasional audible miss, can happen once every 30-60sec, then nothing for a couple mins then once then nothing for a few more mins. It's erratic, but it does happen. No misfire codes occur. I should log it with a wideband to see what the idle afr is.
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