Yes my E60 523 also vibrates when idling. The RPM is stable but like you, I feel the vibration in the seat, and steering and there is the droning noise.
So is yours solved or anyone else has had the problem and solved it? Please share the solution. Thanks.
It seems like quite a common problem for E60...
Idle vibrations E39 540i - United Bimmer Community - BMW Forum
According to the above link, it's caused by the the exhaust mounting.
[FONT="]In the US there is a service bulletin issued for this problem:
"Service Bulletin 18 02 08
Customer may complain of a slight vibration and/or droning noise when the vehicle is idling in park, neutral, drive and reverse when engine is at operating temperature.
CAUSE
Insufficient vibration dampening of the exhaust system.
PROCEDURE
1.Verify the complaint. Vibration/droning is most prevalent when engine is at operating temperature.
2.Remove the lower bracket for the exhaust system. If droning/vibration is gone, proceed to step three. If vibration/droning still exists with the lower bracket removed; continue troubleshooting exhaust/driveline for other causes or conditions
3.Remove complete bracket assembly and replace it with the bracket (1) PN 18 20 7 521 346 using two new ASA bolts (PN 07 12 9 905 417. Tighten to 21Nm.
Install front pipe bracket (1) PN 18 20 7 521 347 with four rubber bushings (2) (PN 18 20 7 546 579) to the new 346 bracket with two ASA bolts (PN 07 12 9 904 559) and two nuts (PN 07 12 9 904 580). Tighten down to 21Nm
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