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Hi everyone. I'm new to the forum and trying to track down a noise on my wife's 2008 DTS. It only occurs on a cold start and gradually decreases and goes away completely as the car comes up to temp. It's not metallic but for lack of a better description it sounds like a hollow plastic on plastic rattle. The strange part is that if you remove the oil filler cap while it's happening it stops. Put the cap back on or cover the hole with your hand it comes back. Currently it has me stumped.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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Welcome to the Funny Farm !!!

Subscribe the car to a multi-year at www.alldatadiy.com - it's the online GM/Cadillac service manuals plus a lot more info.

Might have something to do with the PCV dirty air line - that's the line that connects full intake manifold vacuum to the PCV orifice in the right (rear) cam cover. Check to find out if the plastic line is rattling against something. The clean air line - to atmospheric pressure - connects from the front (left) cam over over to the atmospheric side of the intake ducting at the throttlebody.

Open the oil fill cap and you short-circuit the crankcase vacuum system - replace it or cover the fill hole and vacuum is restored.
 

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Thanks submariner409, I think I can rule out the pcv system. I did the cam cover gaskets last month and made sure all the lines, orifices in the cam covers and o rings were in good shape.
 

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2002 Deville and 2009 DTS
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Is the rattle in front of the driver side wheel? Like under and behind the driver side headlight?

If so, it is the AIR pump.
 

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No it's coming from the top of the motor. At first I thought it may have been timing chain related but when I did the cam cover seals I could see chains, tensioners and guides all looked good. I'm starting to think it may be coming from the PS pump but it's not a noise I would attribute to a failing pump. I guess I'll pull the belt and see if it stops.
 
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