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      02-06-2015, 03:51 PM   #1
richie_s
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Revs dip below 500 RPM during idle in 335i

When the car's all warmed up, it starts to shake a little for a few seconds and the revs drop to as low as 300-400 RPM. Only happens after being in idle @ neutral for about 30+ seconds. Anyone else have this issue with their 335i?

I'm sure I'm not abusing my car because I do everything I can to keep it running nicely

The picture here was actually caught while the revs were rising up from being at about 350RPM.
(Traction control was off because I had to make it up my icy driveway!)
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      02-06-2015, 04:30 PM   #2
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If it sounds smooth, it's usually not a problem. Side of effect of decent engine design, parts and management.
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      02-06-2015, 04:32 PM   #3
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Could be the coils.
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      02-06-2015, 05:05 PM   #4
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Happened to me before, took it to dealer explained what happened like what you described(it shakes at idle) to the guy. Fixed within 3 days. I am not sure what they did but I noticed a new software on my nav.
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      02-08-2015, 01:11 PM   #5
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If there is no misfire and antistall isn't kicking in, what exactly is the problem? There is no mechanical reason why this is a problem, unless caused by an actual problem.
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      02-08-2015, 01:39 PM   #6
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do you have bms intake?
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      02-10-2015, 07:03 PM   #7
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I'm just a weekend diy mechanic but I don't see why it would be a problem.
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      02-12-2015, 05:13 PM   #8
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Quote:
Originally Posted by M-terkait View Post
do you have bms intake?
nope, completely stock vehicle
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      02-13-2015, 06:48 AM   #9
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Vacuum leak.
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      02-14-2015, 03:28 PM   #10
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I read this post and have been looking ar my idle the past couple days and it never gets that low. Even after ive driven it a while.
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      02-21-2015, 05:22 PM   #11
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Take it to the dealer OP. My car starts at 1k+ RPM, and drops down to 750-800 RPM for idle. I live in upstate NY, and it has been COLD the past week (-15 F in the morning). Even though my car is garaged and car starts perfectly fine, it does take a while to warm up.
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      03-28-2015, 04:20 PM   #12
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Alright, I've finally resolved the issue. I gave the car a good "italian tuneup" a.k.a. revving up the engine to blast away carbon deposits and things seem to be running smoothly now. Idle is completely smooth and the low-end torque is more prominent. The engine runs a little smoother.
This makes me think that the rough idle was due to carbon deposit buildup blocking the flow of fuel from direct injection.


All I did was warm up the car for 15 minutes by driving slowly around town and then hopped on the freeway in 3rd gear for a good non-consecutive 30 minutes. The revs were at 4,500 at 70 miles per hour. I exited the freeway and let the car idle every now and then so it wouldn't overheat and hopped back on and continued after the oil temp drop a little.

Last edited by richie_s; 03-28-2015 at 08:21 PM..
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      03-28-2015, 04:23 PM   #13
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Quote:
Originally Posted by M-terkait View Post
do you have bms intake?

nope- completely stock. I'm guessing the rough idle was just caused by crap loads of carbon buildup. My daily commute is really short and my car often sees temps below freezing, so there's no surprise there. I also rarely stretch its legs... i keep the revs below 3,000 RPM 99% of the time.
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      03-28-2015, 04:35 PM   #14
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Quote:
Originally Posted by richie_s View Post
nope- completely stock. I'm guessing the rough idle was just caused by crap loads of carbon buildup. My daily commute is really short and my car often sees temps below freezing, so there's no surprise there. I also rarely stretch its legs... i keep the revs below 3,000 RPM 99% of the time.
oh ok everyday i extend my 5 km to work to 10 km trip just to go from 70-190 kmph almost everyday i do it
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      03-28-2015, 08:07 PM   #15
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Quote:
Originally Posted by M-terkait View Post
oh ok everyday i extend my 5 km to work to 10 km trip just to go from 70-190 kmph almost everyday i do it
Maybe I should find a longer commute and do a 0-100 kph test run every day from now on to stop this from happening again
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      03-28-2015, 08:17 PM   #16
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Quote:
Originally Posted by 34.50 View Post
Take it to the dealer OP. My car starts at 1k+ RPM, and drops down to 750-800 RPM for idle. I live in upstate NY, and it has been COLD the past week (-15 F in the morning). Even though my car is garaged and car starts perfectly fine, it does take a while to warm up.
you should watch out for carbon deposits too. I live in a cold area just like you (frequent morning temps of single digits or negatives) and I'm more than 100% sure that the extreme cold mixed with my short commute lead to nasty carbon buildup that ruined my idle. it's better to prevent the problem than to fix it.

now I use fuel system cleaners and run my car really hot (5k RPM) every now and then to blast out the carbon deposits. just make sure to switch out your oil and oil filter regularly because some carbon chunks get dispersed in your oil.

I'm so glad I found out about these techniques
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