Description of the problem (By the way, I'm just approximating engine RPM in my description)

(2006 / 550 / 49,000mi / automatic / no codes or warning lights ever)

Start-up:

RPM starts at about 1000 for 30 seconds, then drops to around 500. RPM's remain stable during initial idle.

Driving:

No noticeable issues.

Stopped:

Once I come to a stop (car in drive) the RPM goes back to 500 for a moment. Then it drops to just below 500, then goes back to 500. While the RPM is fluctuating, you can feel/hear a low humming vibration. Almost like a super throaty exhaust sound. Once RPM's return, the sound goes away. Usually it will just cycle through once and then the idle will stabilize, but sometimes it will cycle through 500-450-500 a few times. Especially, if I'm creeping along in traffic.

It all stops once you give it gas or let the car roll forward and acceleration seems normal. however, stopping brings it on again. Shifting into park also makes the drone go away.

None of his happens when the A/C compressor is on. With the compressor on, the RPM is super stable at @ 800 or so. No fluctuation. No droning sound.

FYI... I am definitely leaking some oil from the brake vacuum pump or the corresponding line below. By the looks of the pan below the engine, it's leaking pretty nicely, but no low oil warnings yet. It's scheduled to go into the dealer for the warranty "fix" next week. I plan on sealing the pump housing myself if that indeed is the source of the leak and will probably ask them to check the idle, but as I am out of warranty and as I tend to be a DIY'r, I'd rather not have the dealer guess at what may be wrong.

Anyway, can these two issues be related? Am I losing vacuum pressure through the brake pump, which is causing my rpm's to be erratic at idle?
It's been real cold here (below freezing) for weeks and lately it warmed back up to over 50. This just started over the past weekend.

Anyone else here have a similar issue? I've read about some with a similar problem, however, never saw a conclusion...

Any info would be appreciated!

/jack

 

Hi Jack,

I've been doing some research and happen to come across your post. I have a 2007 550i with the exact symptoms you described with your idle. My idle only seems to dip below 500rpm when braking to a stop as well. Just wondering what the cause/fix was in your case. Any details would be greatly appreciated!

Thanks,

Dave

 

I had the same issue. Dealer updated some software and it was resolved for the most part. My car still idles a little too high with the A/C on.

 

My 2007 550i has a bit of a rough idle..not sure if it mimicks the above exactly, but it has a rolling/cammy feel. Dealer stated it was nothing.

I also get a fair amount of 'soot' on my rear fascia (white car). Dealer also said it was normal. I go thru about 1 qt of oil every 7k miles.

 

One thing that I've realized may cause rough idle - the MAF sensor. It may not throw any codes, but try buying the MAF cleaning spray from your local auto parts store and cleaning yours before you spend any more money on anything. If the idle problem disappears/improves after you clean the sensor, there's your solution. Unfortunately, it only works for a few days, and you'll have to either clean it again, or pony up the dough for a new one.

I posted a DIY for cleaning your MAF sensor a while back, so a quick search and you have your instructions, should you need them Pretty easy stuff - two torx screws, and you just have to be careful not to damage the delicate parts on the MAF sensor.



If MAF sensor cleaning doesn't help, it could be something "along the serpentine belt" - meaning, either the pulley isn't turning very well anymore, or smth like that.

If it's running rough, in a way that is resembling misfiring, it could be spark plugs and/or coils.

 

Thanks for the feedback guys! Going to start with cleaning the MAF. If that doesn't pan out, guess I'll have to hit the dealer.

 

Hello,
My 550 is rough on initial start up which is common from the "vanos", but if its still doing this after its warmed up then that is strange. for your brake leak make sure your car has been serviced for the "recall" all 45 and 50 models had a warranty recall and will be fixed at no cost!

GL

 

I don't have any leaks and the car runs great. No misfires or anything but it's just strange that the idle settles to 500rpm after braking to a stop and then it dips down just below that for a few seconds; low enough for a noticeable vibration. After that, it settles back up to 500rpm and is solid. It does this every time I come to a stop when the car has warmed up. Since there are no codes/warning lights, I'm reluctant to bring it in to the dealer because it will most likely result in a huge waste of time.

 

MAF is possibly dirty, have in mind BMW V8 characteristically are known do fluctuate a little at idle which is normal. The normal range is +/- 25 with the 500RPM as your base line.

Like I said MAF has a lot to do with this and unfortunatly if it is dirty it wont show you error codes :thumbsdown:

Hope this helped

 

Thanks much for the input. I haven't had a chance to check out the MAF yet so hopefully I can get to it by this weekend.