How big is your tool box?
You can move the fuel injector to another location. Better yet, ohm each injector. Check for ohm differences. You can use a special tool to monitor fuel injection pulse. I have a Power Probe IV with a pulse feature. The injector could be leaking too. How many miles are on it?

Worst case, the head gasket may be starting to fail. Do you have a mysterious coolant loss? Check compression on a hot cylinder.

Is the coil a good brand? Why type of spark plugs are you running?

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'06 X5 3.0i - bought @143,123 miles (12/26/20)