Dealer fixed the idle vibration
Ok, I was able to get the dreaded low idle vibration fixed on my 2008 528i. I did some research and found out that there is a bmw service bulletin that describes this problem. The service bulletin number is 18 02 08. (see the description of the bulletin below)
After 2 previous attempts at getting this problem fixed at two different dealerships, the 3rd time was a charm. As usual they initially tried to blow me off and tell me that the booming idle was normal. Then I insisted that they look at the car with the service bulletin that I handed them. The end result was that my idle is now nice and smooth. The problem is not that the idle is too low, but that the problem has to do with the exhaust system vibration. The following is the actual text of the service bulletin:
"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.
Insufficient vibration dampening of the exhaust system.
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
After performing this procedure the vehicle will exhibit the same amount of normal driveline vibration as a comparably equipped E60 with a M54 or N52 engine."
Now what follows is the exact wording from the invoice of what the dealer did to repair my car:
“Insufficient vibration dampening of the exhaust system. As per service bulletin 18 02 08, verified vibration, removed lower bracket from exhaust system, vibration no longer present, removed and replaced complete exhaust bracket assembly and replaced exhaust vibration dampener, test drove vehicle OK. Defect Code: 18 11 00 39 00 Labor op: 18 99 000”
I hope this helps. This was a real pain, but I am very happy with the result. Let us know if it works for you.