Rough Idle On Cold Days?

[Weebie]

I have a 2006 X5 E53 4.8is and I get a rough idle when it is really cold outside. It does not seem to be a cold start issue as the problem is still apparent when I've driven the car for well over an hour.

I know the 4.8is has a bigger exhaust and it seems like the cold weather is causing the exhaust to rumble, which causes my car to shake and vibrate very rough. The vibrations feel like my X5 has message chairs and the steering wheel shakes. The rough idle is more apparent when the car is stopped at a stoplight with the engine engaged in drive. The vibrations lessen when I put it to neutral and park.

I've taken the car to a couple dealers already and when they hooked it up to the computer there were no error codes, engine misfires, and etc. It checks up as everything is running fine so they have no idea what is wrong.

So here is my question for all the other 4.8is owners on here. Is what I am experiencing normal for the 4.8is in the cold winters due to the larger exhaust? Or is there something really wrong with my X5? I don't experience these rough idles when the weather is warm.

Any suggestions and input would be greatly appreciated.

TIA