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Discussion Starter #1
2009 2.5l convertible making loud humming sound when air is on ( sometimes). Mechanic says it’s too much crankcase vacuum after he pulled dip stick and oil fill cap and heard sucking sound. I replaced valve cover/pcv valve, and it changed nothing. When I pull the oil cap it idles rough. Any suggestions? I’m scared the excessive vacuum will cause leaks, but the humming sound is driving me crazy!
 

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Isn't it normal for a car to idle rough with the oil cap/dipstick out?

Pretty sure mine does the same thing b/c your opening a closed system letting air in/out.
 

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You said the humming sound is when the air is on?

Might be a blower motor going out? Sound like this:
 

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Discussion Starter #4
It’s not the blower. Best I can tell, it seems to be coming from a copper/gold colored block vibrating on the fire wall where the a/c lines go into the fire wall. Maybe? As far as the oil cap goes, I’m not sure if it’s supposed to do that or not....
 
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