Please add the year and model in your signature--helps a bunch when responding rather than searching the thread.

A significant oil leak depending on the source, like valve covers, can pool in a spark plug hole and short out the plug with a resulting misfire---rough and sporadic idle.

Vacuum leaks are not uncommon. Again, depending on the source they can cause misfires and other problems. I put the smoke test among the first troubleshooting tests to find core cause of an engine issue. Good that you are having that done.

The list of potential sources of vacuum leaks is long and sometimes depends on what engine you have. I suggest waiting for the results of the smoke test. Vacuum leaks generate a lot of different sounds, I haven't heard any I would call a growl but definitions and what we hear widely varies. There are also a wide range of other causes for a growl sound. Does the engine rev normally?

I would clean anywhere you can see oil on the engine and by the time you get the smoke test it could help to verify where it is leaking--good time to check for both.

It is a good practice to use a quality brand of fuel with a cleaning agent. As an example, I alway buy gas that has Techron and in addition periodically add a bottle of Techron to a full tank of gas.

Is the vibration at 2000rpms when moving or when revving the engine?

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas