RTR

The noise comes after a cold start (car's been sitting for 2h+), goes away in about 30-40 seconds. BUT, it I turn it on, turn it off right away and restart it, there is no noise...
I thought it might be a serpentine belt or a bearing on water pump/alternator/power steering pump, but the noise is still there after spraying the belt with water. Took off the belt, inspected every pulley there, only WP is slightly squeaking. But that fact that it goes away after the restart doesn't make sense. (I'll try to start the car without the belt for 3-5 sec and see if the noise would still be there and let everyone know).
Vacuum leaks? Inspected everything from air box to throttle body, couldn't see any cracks. Tried spraying with brake cleaner. Should I take it to a mechanic to do smoke test?
Read on another forum that a high pitch noise was caused by a failed CCV. Checked mine, they looked a bit dirty, but not ruptured. Cleaned and reinstalled.
HVAC on/off doesn't make a difference.
The sound doesn't seem to change with throttle. During these 30-40 sec it may stop for a few seconds and then start again.


Right now I have no idea what's going on. If I can't figure anything out with your help guys, I guess I'll take it to the mechanic.

Background info (maybe some stuff is related to this):
Changed vacuum pump, changed oil pressure sensor, changed spark plugs (although the noise started before it).
I have fluctuating rpm at idle (cold engine, warmed up engine, doesn't matter. The fluctuation is only about 50-70 rmps though), have a P0491 code for secondary air supply (most likely cracked y pipe, but will check it out soon), very significant vacuum if I open oil cap (car even stalled once).

Car: 2004 545i 110k

Please let me know your thoughts, if I can do some other tests. Btw, I also have INPA and DIS software.

Thanks!

AchtungE60

Letting car sit for 3 hours after driving isn't really a cold start since the car has already been at operating temp and usually wont come down for about 5 hours or so.
Fluctuating RPM is a sign of intake issue, maybe a vacuum leak.
If you have DIS and INPA then you shouldn't have a problem finding the source unless it's physical. In fact, you probably can tell me about the car logically than any mechanic besides a BMW dealer or INDY can.

The car should never ever go to 50-70 rpms the lowest is about 400-500. I think idle is about 500-600, so the ICV is something to take into consideration.
If you take the valve cover cap off, you're breaking the sealed system and you can expect the car to hiccup, sputter and probably stall out.

RTR

AchtungE60
Thanks for the reply. I meant it idles at set idle ± 50-70 rpm (I think DIS showed that the idle is set at 450), so it usually goes up&down between like 420 and 480.
I read on another forum that slight vacuum at the oil cap is normal, but if it sucks A LOT of air in, it might be a failed CCV.

INPA / DIS do not show anything abnormal (well, at least I don't see anything). Would appreciate it anyone could tell me what to look for exactly.

Reason I wrote "cold start" is because it all started about 3 months ago and the sound would be only when the car's been sitting overnight. Then it started to appear more and more frequently.

AchtungE60

I think it's intake/spark related.
Clean your MAFS, Check your filter to make sure it's not clogged up. Have you driven through any dirty dusty regions?

When is the last time you changed plugs?
Have you tested coils?


In DIS you may not get errors but you can check the true running value of the cylinders and see which one is lagging and also if it lags at idle or driving RPM. Also about RPM you should just say 500 RPM not 50. Because your RPM are 1-7 x1000. This is why i was confused. When you say 50 your technically saying 50x1000 and at 50,000 I would think you'd have no engine. So at just 50 I thought you were surging from 500 to 50 which is a problem.
Anyway probably best to change plugs if you never have and at that age/mileage you're overdue for a basic tune-up anyway.

Also you said you tried brake cleaner...what was that for? Is that supposed to simulate a smoke test or something?

RTR

New air filter, already cleaned MAF, new spark plugs (everything started before I did all of that), coils - not sure.

I can't believe I forgot one more thing... If the car is cold and is let to idle right after start, it would start misfiring after about 30 sec. If I restart it right away or just start driving after the cold start, it doesn't misfire. Only cylinders 4 and 8 misfire. Swapped the coils between cylinders 7 and 8, made no difference, still 4 and 8.

I tried looking at cylinder roughness, there are none out of order (very slight fluctuation in all cylinders), but if the cold car idles, 4&8 show crazy roughness.

Brake cleaner: just spray in areas that might have vacuum leaks (plastic hoses, connections, etc) and listen to engine idle. If it changes - you found a leak. Although not very effective for small leaks or ones that are not easily accessible. Be warned though, some say there is a very slight chance of engine catching fire. The difference is very small, but it gives the idea. The car wants to maintain stable rpm, but actual rpm is different


Misfire codes:



For cylinder 4 it says exhaust-gas-related misfire, for #4 just misfire with cylinder cutout. Does it help in any way?

AchtungE60

Don't every use brake cleaner for this test. If you're checking the o-rings on injectors I can understand but I still wouldnt be using brake cleaner.
For the misfires, you have an issue at the intake by the manifold so drive around with the diagnostic machine hooked up and read the values in real time and I bet you the misfiring will go away when past 1000 RPM or so. This would confirm my diagnosis.
As far as fix that remains to be determined I have to look at your type of engine first. Could be an electronic air controller at idle or it could be a simple o-ring not good etc.

AchtungE60

where do this come into play on your car? before the throttle body?
http://realoem.com/b...278&hg=11&fg=45

Hard to determine without the entire picture.
http://realoem.com/bmw/showparts.do?...77&hg=11&fg=40

RTR

If it starts misfiring I usually just restart the car. Once I kept driving and it went away after 1-2 min.

Not sure I know what you mean. The vacuum pump has 2 hoses, one goes to the brake booster and I'm not sure about the other one, but can check.

Another thought it is the DISA. Any way to diagnose it?
Don't want to take the whole intake manifold to find out it's perfectly fine.

saltdog

I had the same whistle sound which was air traveling through a crack in the pressure regulating valve. See the DIY below. It's very easy.

https://5series.net/forums/topic/853...gulating+valve

RTR

Thanks for the tip!
I checked them 2 times before and they looked fine. Checked again today and there are no cracks I can see... Anyways, I'll probably just replace it.