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      12-05-2012, 10:53 AM   #1
sammk
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328i N51 unsteady idle potential fix

For the longest time I had a rough idle on my 2008 SULEV 328i, N51B30. I looked into all kinds of possible issues but wasn't able to diagnose the issue. If you're driving along and come to a stop, the idle would settle in, but the rpm would bounce by 2-300 rpm randomly and intermittently. Needless to say, there were unpleasant vibrations and noises when this happened. This was happening when the car was still under warranty at 30000 mi, and the dealer tried a few things but nothing worked (there was no fault code or SES light). They finally ended up increasing the idle speed to 650 rpm at my request so that the unpleasant vibrations would at least be minimized, but the problem continued. I contemplated getting the intake valves blasted but realized that would be useless on a Port Fuel Injected engine like the N51/N52.

Fast forward 1.5 years and 20000 mi (2 miles after my car ticked over 50000 mi to be precise), and I'm sitting in the car, idling outside a restaurant, buckling down and getting ready to leave when the whole car starts shaking like a mutha-f*** and the SES light comes on. I curse the curse of the rough idle, drive to Autozone and pull codes. P00BC (MAF sensor too low) and P0305 (Cyl 5 misfire). I proceed to clear codes to see if it will return. I decide to attack the Cyl 5 misfire first, so I get home and pull the #5 coil. Check static DC resistances on all 6 coils, and they're all similar, #5 does not stand out. Before I pull the trigger on plugs or coils, I decide to give it one more chance. So I put a little bit of dielectric grease on all boots, interchange #1 and #5 coils and put everything back nicey-tightey.

After about 250 miles of driving since, my idle has not been smoother ever. The car purrs when idling at 650 rpm every single time and idle speed is mostly rock-solid. There's a slight movement occasionally but that's normal due to idle air compensation.

So if any of you guys/gals is getting a premature misfire fault or experiencing bad idle at low miles on the N51/N52 motors without the SES, check and lubricate your coil boots. Might or might not be the issue, but could be a potential fix..

Enjoy!
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      12-05-2012, 11:16 AM   #2
Buckeye85
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Thanks for posting. Maybe this will fix my idle at stops. Vibrates door and seat, wheel. I can not stand this POS for much longer. I have had 2 dealerships and a great indy shop come up blank on the rough idle.
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      12-07-2012, 11:03 AM   #3
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Yeah, let us know how it works out. I'm interested to know if others have the same issue as well.

Added note - I have about 500 miles since I did this, and the idle is holding out rock-steady. I was hoping that once I corrected the misfire issue I had earlier, my mileage would go up a tick. I've been through a tankful since and that doesn't appear to be the case. Not that I noticed any signs of misfire previously - just an added thought, that's all.
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      12-07-2012, 10:21 PM   #4
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Good find, adding to the list of maintenance things to be done...
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      12-08-2012, 01:16 AM   #5
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i have a 2011 328i and my car shakes like what ur describing
im going to the dealership tomorrow so what should i tell them?
i also have 3000 miles on it.
also here is my thread with a vid.
let me know if this is how your car is also

http://www.e90post.com/forums/showthread.php?p=13114569

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      12-13-2012, 02:53 PM   #6
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How exactly do you check the resistance, and add the grease?
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      12-13-2012, 02:56 PM   #7
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DIY is needed
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      12-13-2012, 08:10 PM   #8
sammk
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Folks - sorry I've not been paying attention to the forum. Just saw the thread was bumped..

Quote:
Originally Posted by werd View Post
Good find, adding to the list of maintenance things to be done...
Yep, that's a good idea.. It seems like rough idle is a common issue with this engine/car, so preventive maintenance should be helpful, especially as those miles pile on.

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Originally Posted by Mattshokri View Post
i have a 2011 328i and my car shakes like what ur describing
im going to the dealership tomorrow so what should i tell them?
i also have 3000 miles on it.
also here is my thread with a vid.
let me know if this is how your car is also

http://www.e90post.com/forums/showthread.php?p=13114569
Damn, that's bad! Mine was similar but not quite as bad. You definitely have a possible misfire or a MAF issue going on. Mine was similar but it would get bad, settle into a decent idle by itself for a few seconds, then get bad again. My idle speed never bounced up that high, it would always drop, bounce slightly higher than normal, settle in, then do it all over..

Was the dealer able to diagnose/fix the issue? If not, you could ask them to inspect all 6 spark plugs and coils, and check for pending misfire codes (that don't light up SES light).. Your issue could also be MAF related, so I would ask them to check the MAF connections and cleanliness. If they find the MAF was the culprit, and your car is under warranty, I would request a new MAF sensor, those things are finicky and don't like getting cleaned always.

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Originally Posted by dylim View Post
How exactly do you check the resistance, and add the grease?
Once you have the coil out, there are three electrical contacts. I grabbed a multimeter and set it to measure DC resistance in the 0-20 Ohm range. Two of the three electrical contacts will give a reading for resistance. Mine were in the 1.9 - 2.0 Ohm range IIRC, I could be wrong on the numbers. I guess it's more important that all 6 measure about the same, if one or two are off, those are probably bad/going bad.. I'm not sure this is the 'official' way to diagnose coils, I'm sure BMW's service literature will show the correct way to diagnose the health of coils.

For the grease, just dab a little bit around the end of the coil boot (which goes over and around the spark plug top), press it in firmly and call it good. It's mainly to keep moisture and dirt away, and ensure good conductive contact with the spark plug.. You don't have to go gangbusters, just one of those little pouches for all six cylinders should do..

Quote:
Originally Posted by ERIC212NYC View Post
DIY is needed
Noted, I didn't take pictures, so I can't make a DIY, but the next time I get a chance I will try to tear things apart again and get pics to make a DIY.. There's a good vid on Youtube that shows you most of what to remove and in what order:



Hope this helps! If you have similar experiences, please do share..
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      12-14-2012, 02:09 PM   #9
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Thanks Sammk!! Going to try this soon, the rough idle is driving me crazy...
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      12-14-2012, 02:27 PM   #10
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You're welcome Dylim, hope you're able to fix the issue one way or another..!

600 miles under my belt and the good idle continues. I did realize something however - my M54 E46 was and is still the benchmark for silky-smooth idle.. I think those of you who came from E46s may agree.
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      01-07-2013, 04:10 PM   #11
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Seems like the rough idle is gone! I need to drive more to confirm, but seems good so far. I replaced the spark plugs, and coated the entire ceramic (white) part of the plugs with a thin layer of the grease (according to the label instructions). The grease I got did not come with a needle head, so I was not able to coat the inside of the coil boots, but I added a small dab at the end of each boot, following Sammk's instructions.

I noticed there were some signs of oil around the engine, so I'll probably replace the valve gasket next time I get in there. Also want to clean up the dust and grease around the engine.
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      01-07-2013, 09:47 PM   #12
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Quote:
Originally Posted by dylim View Post
Seems like the rough idle is gone! I need to drive more to confirm, but seems good so far. I replaced the spark plugs, and coated the entire ceramic (white) part of the plugs with a thin layer of the grease (according to the label instructions). The grease I got did not come with a needle head, so I was not able to coat the inside of the coil boots, but I added a small dab at the end of each boot, following Sammk's instructions.

I noticed there were some signs of oil around the engine, so I'll probably replace the valve gasket next time I get in there. Also want to clean up the dust and grease around the engine.
Sweet! Hope that it stays that way for you and let us know after you get some miles.

Couple thousand miles later I'm going strong..
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      02-05-2013, 12:14 PM   #13
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Is there a way to diagnose the exact cause of the rough idle? I'm experiencing the same issue with my 2006 330xi when at idle in Drive or Reverse. The issue doesn't occur when in Neutral or Park.

I've read that it can be a dirty MAS, plugs, wires, Vanos or the Valvetronic Sensor. Is there a way to nail down the culprit without a fault code? I had one of the Vanos replaced already before I bought the car because of it throwing a code.

I would have started my own thread, but I'm not allowed, so I figured that since this one was resolved, I wouldn't be hijacking.

sammk, I love your Kat. I have one too.

Video of issue:

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      02-05-2013, 05:52 PM   #14
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Thanks for this information!
My idle is not as rough as it used to be, here and there it acts weird and minor vibes, I did replace all 6 coils and plugs and MAF this past summer. No difference really. A hair smoother but at least that part of the maintenance is out of the way.
As soon as it get a bit warmer out i without a doubt will pull the cover off and grease up them coils.
You may have discovered a cure for a lot of people with symptoms they never could remedy.
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      02-19-2013, 04:34 PM   #15
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Quote:
Originally Posted by Spyderturbo007 View Post
Is there a way to diagnose the exact cause of the rough idle? I'm experiencing the same issue with my 2006 330xi when at idle in Drive or Reverse. The issue doesn't occur when in Neutral or Park.

I've read that it can be a dirty MAS, plugs, wires, Vanos or the Valvetronic Sensor. Is there a way to nail down the culprit without a fault code? I had one of the Vanos replaced already before I bought the car because of it throwing a code.

I would have started my own thread, but I'm not allowed, so I figured that since this one was resolved, I wouldn't be hijacking.

sammk, I love your Kat. I have one too.

Video of issue:

Not sure how exactly to pinpoint. To add to your list of possible causes, I've read that some people had leaking PCV pipes or other hoses, leaking valve gasket, oil-soaked eccentric shaft sensor, oil change gone wrong - oil cap wasn't torqued down properly, or seals cracked/not replaced, or lower quality oil (my nearest bmw dealership uses cheap, non LL01 oil!).
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