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odd rattling


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My STS for hte last 5 months now has been rattling severely at idle. It doesnt really bother me, but it makes the car sound really poor. Its only at 500ish rpm, once I touch the gas slightly, or drive normally, this rattle is gone. I dont know if its a pulley..or what. I have no idea. Any input is greatly appreaciated

Thanks, Mike

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I believe your problem is the idle is too low !

600 should be the correct idle with A/C off (650-75 when compressor is running)

Any codes ?. they might hold an answer (like IAC going bad or bad PCV/EGR)

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Mine had a rattle just off idle at about 750 rpm with the brakes on and the transmission in gear. It was coming from under the car in the center at the front of the cabin.

This is the area where the exhaust pipe from the rear cylinder bank comes down, bends rearward, then enters the catalytic converter. There are exhaust pipe heat shields on the firewall side of the exhaust pipe and the clearances are so tight that it's hard to see what's going on, much less get your hand in there to do anything about it.

I suspected that the heat shields were vibrating against the exhaust pipe, the body, or each other. I had a muffler shop look at it and they pushed things around and tack-welded the shields. This seemed to help a little but the rattle didn't go away completely.

Late last year, I had the engine taken out of the car to replace the head gaskets. When I got the car back, the rattle was completely gone!

Pulling your engine to stop a rattle would be total over-kill, of course but I suspect the rattle you describe has to do with the exhaust pipe, heat shields, and/or bodywork in that tight space between the engine and the firewall.

If you can get the car up on a hoist with someone in it to run the engine at the right speed with the car in gear and the brakes on while you and/or a muffler man poke around the heat shields underneath, you may be able to locate the source of the rattle.

Good luck -- I know the problem isn't life-threatening put it sure is annoying! :(


Happiness is owning a Cadillac with no codes.

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