540 i whistling sound at idle

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firebird93

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#1
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#1
ok all you bmw gurus out there i need some help
my wife has an 01 540 i and recently it has started on occassion making a strange whistling or squealing sound at idle and seems to run slightly rough when it does it. it will do it a few seconds then quit and engine smooths out. i sounds like it is coming from front of engine but i can't isolate it. just when i think i might be getting close it quits. any help will be appreciated

dh
 
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firebird93

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#3
this is not what i would call alternator whine it is very loud and no problem for anyone within 100 ft to hear. but like i said it happens on occasion and goes away if u increase rpm and will usually last only a few seconds without increasing engine speed.


dh
 
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Big Daddy

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#4
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Vacuum leak maybe? Check the boot between the MAF and the engine, they can split in the accordion like folds. Also do you have an appendage on your factory air filter box?
 
E30m42cab

E30m42cab

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An '01 boot wouldn't be ready to crack yet though, unless it was really stressed when taking the filter box off. Maybe the serpentine belt tensioner? (I know nothing of BMW V8's, but we're all guessing here) I wouldn't think it would be your starter gear staying engaged on the flywheel too long would it?
 
CosmosBlack

CosmosBlack

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Just like Big Daddy said, possible vacuum leak....Whistling sound could very well be from the Oil Separator starting to turn bad,
and more so with the rough idling you mentioned.
 
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firebird93

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#7
oil seperator ??? tell me more about this because it has started to puff a little white smoke on startup since this started.

dh
 
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MMLJTIGER

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#8
540 whine

Hi there,

The oil separator is, basically, a PCV valve. It's a pain in the ass to get to, because it's under the intake manifold and requires removal of the throttle body... a biggish job to do.
I have a question first:
Have you ever done/had a coolant flush? (Reason being that over time coolant turns acidic, and can affect things like the water pump bearings.)
Does the noise happen hot and cold
You could take a long screwdriver and put the tip up against the water pump body. Thru conduction, to your ear, you might be able to hear it.
I'd personally start there, if I were you.
Hope this helps,
Tiger
 
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pythias

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#12
i just bought a 1994 318i BMW.when i drive it below 15litres. in the morning it fails to start.sometimes the fuel pump fails to start.recenty it cut the fuel when i was driving and could not start anymore
 
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