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Discussion Starter · #1 ·
FYI: 2014 X5 3.0 S-drive with whistle noise from engine, rough idle and driving for the past week or two.
Opened hood, as soon as you open oil cap with engine still running, whistle goes away.
That is the perfect description/diagnosis of a failed valve cover with the integrated PCV valve on N55 and some other BMW engines.

The car also had to be jumped twice earlier in the week. I was just about to buy the ~$11 PCV do-it-yourself kit to cut/pry off the old and affix the new one, when I also changed the battery.

***Problem solved with a new battery. No more whistling, no more rough idle/engine miss.

Something in the engine, PCV vacuum system, or whatever needs to be running at the correct voltage or is finicky to a dying battery. This repair was done 3 months ago already with no recurrence so I don't know if it could help someone else rule out this as a long-shot possibility. Maybe test engine with another battery before changing the whole valve cover/PCV which can cost up to and over for $1000 for some people. Makes me wonder how many of these were changed unnecessarily or what about a failing battery causes the whistling/PCV vacuum problem.
 

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How old was your battery, assuming it was the original. What size is it & one or two batteries? Did you change it yourself? And register it? Just curious. Did any info center message you that the battery was going bad/weak?
 

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Discussion Starter · #3 ·
How old was your battery, assuming it was the original. What size is it & one or two batteries? Did you change it yourself? And register it? Just curious. Did any info center message you that the battery was going bad/weak?
The battery must have been 7 years old. I know the battery was going weak because I needed a jumpstart 2 or 3 times. It also tested bad at 2 different places. I replaced it with an H8, which was later coded/registered.

The whistling was fixed even before the battery was registered/coded. My X5 has one battery in the back near the tailgate under the carpet. Not hard, but a lot of brackets/bolts, etc to remove and put back.

I just found it useful to mention that the infamous PCV/valve cover whistle could be caused by a dying battery.

Not going to be the case for everyone, but I had just ordered the PCV repair kit because the tell-tale sign of the whistle going away when opening the oil cap would happen, etc. If that didn't work, I would have gone for the whole integrated valve cover. I luckily canceled the order in time. Would have been a complete waste of time because even several months later, the problem has never come back.

May be useful for someone with troubleshooting before replacing parts unnecessarily. I can't even comment on how a low battery affects the PCV system to do this, just that it does.
 

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I sincerely hope your issue is resolved.
Very strange as vent valves don’t have mush to do with battery voltage. Please keep us updated
 

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Discussion Starter · #5 ·
I sincerely hope your issue is resolved.
I suspect it’s not. Crankcase valves can be intermittent and doesn’t really have anything to do with battery voltage that I can think of. Please keep us posted as I’m very curious about this one
It's been over 4 months and stopped as soon as the battery was changed. I can pretty much say the "issue is fixed" with not one recurrence versus the serious amount of howling PCV every time the vehicle is being driven for every single day of the week leading up to the battery change. How? Why? Electrical PCV pump or something that was getting under 12volts to not create enough vacuum, leading to the whistling??? Electrical PCV valve heater not activating is a better guess leading to incorrect vacuum pressure? That's a part that doesn't even exist in many other vehicles and just goes to show the complexity involved and why I didn't try to figure it out. I am not a 'licensed' mechanic, but am pretty capable and do a lot of work on vehicles. I would have done the PCV repair kit myself and the entire valve cover it that didn't work.

The only conclusion I can come up with is that a dying battery can cause the PCV/valve cover whistling that stops when you take off the oil cap. Initially, it seems unrelated, and is just something to look out for before spending big on repairs.
 
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