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My car shakes constantly. Upon startup, it is very noticable through the driver's seat.

It's obvious when accelerating also. It seems to be coming from the front end, but I honestly can't be sure when giving it gas.

It really vibrates when braking. While braking, it doesn't vibrate through the brake pedal or steering wheel. It does not pull to one side. Again, it seems the front end of car is shaking.

I've searched the archives and only gave myself a headache. I'm not sure if this is a symptom of bad MAFs, cam sensors, a broken engine mount, suspension parts, or bad cat(s), or...

Also, when I was cruising a about 45mph, I decided to put the car into neutral to experiment. Sure enough, the car vibrates. But! While revving in neutral to about 4500 rpms at about 45 mph, the vibration does not get worse.

It does not get worse with higher speeds.

At this point, I'll take any and all guesses. What can I check for before going to the professionals?

There are no idiot lights (like SES) showing.

It has 47500 miles on the odometer. There were 46880 when I bought it.

P.S. I'm the second owner of this car, and this is my 2nd '03 M5. I bought it through a dealership. It is CPO'd. I checked for bodywork and found none. I paid particular attention to the engine bay, the trunk, and the inside of doors. All of these areas looked intact and "factory". (It appeared to me like the previous took great care of this vehicle: the wood trim was scratch-free, and the driver's seat looked barely used.) On a a paranoid note, there's no way a dealer would CPO a car with frame damage, right?
 

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About dealers: There are many dealers who would do anything to make a quick buck, including outright fraud.

I do not thing CPO means anything, except you get a limited extended warranty.

If the car is CPO, just take it to the dealer to fix the vibration.

A few questions:

1. Can you feel the vibration when the car stands still with engine running?

2. Does the vibration change with varying RPM at standstill with clutch pedal pressed?

3. Does the vibration change with varying RPM at standstill with clutch pedal released and gearbox in neutral?

4. How does vibration vary with road speed in each of the different gears?

5. If you drive at speed, and declutch and let the engine idle, does the vibration change?

6. If you drive, and the switch off the engine while the car is still at speed (BE VERY CAREFUL NOT TO ENGAGE THE STEERING WHEEL LOCK) does the vibration change?

7. If the car is parked, engine off, and you push down one corner of the car at a time and bring it to bounce by repeadedly pushing the corner down, and the stop pushing, does the car settle immediately, or does it continue to bounce up and down for a brief moment? (this is to check the shock absorbers)

David
 
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