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  #1  
Old 05-04-2004, 08:01 PM
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Motor Mount?

On my 2001 C320, ill get in my car in the morning and start up my car, it idles at 1200 for about 20-30 seconds then slowly decreases the RPM,, When it gets to 700-800 RPM, there is the low frequency vibration in the car that is in some wierd way audible almost like a faint low bass sound you would get from a sound system.....

However after 10 minutes of it idling it goes away,, Does anyone know what this is, or how i can correct this??

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Old 05-05-2004, 12:39 PM
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?
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Old 05-06-2004, 10:18 AM
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hmmm,
My SL320 has an air pump that starts up right after you start the car when it is cold, I don't know if your newer car has that or not, it sounds like a vacuum cleaner. Does the sound occur when the radio is powered off? and why do you mention motor mount in your title? The decreasing idle after start up is normal. Good luck!
Brian
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Old 05-06-2004, 10:24 AM
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The sound occurs when the radio is on or off, I know for a fact it has nothing to do with the audio system,, i was just using the audio system to give a comparison to the sound i was hearing.,, the reason why i mentioned the motor mount was because in my last mercedes, a similar problem occured and it was the motor mount. I understand that the idle decreasing is normal. I was just giving the forum a play by play of what and when things were happening.. I hear something start up when the car is started, maybe its the airpump,,, but the low frequency vibration is a whole other problem.
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  #5  
Old 05-06-2004, 10:39 AM
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Does the sound change if you put the transmission in gear with your foot on the brake?
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  #6  
Old 05-06-2004, 11:40 AM
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Just slightly, because the rpm goes down very very slightly
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  #7  
Old 05-06-2004, 12:02 PM
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Evan

Have you checked your exhaust system and expecially the the rubber hangers? You could be missing one or it could be torn.

Can you determine what part of the car it is coming from?

If you have bad motor mounts, often a trained eye can tell by the lack of space between the oil pan and the front suspension cross piece.

On the old 190e I discovered that there was less than a inch. Once replaced the clearance has almost doubled.

Haasman
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Old 05-06-2004, 02:28 PM
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if it is a motor-mount, what method would you use to slightly take the pressure off the mounts and listen for the sound to go away?

can you use a floor jack and a piece of wood to slightly lift the engine ( across sump? ) ?
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Old 05-07-2004, 01:12 AM
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Yes you can. Just be sure to only take the pressure off and not lift too much. A general rule is if you can put fingers in between the cross member and the bottom of the engine, the mounts are gone.

Haasman

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