I agree with all the suggestions here. Another thing you can do is pull the plug and see what it looks like. Is it fouled out with carbon or oil? Electrode worn out? Plenty of info out there on how plugs tell a story. Also, as mentioned by others, the top half of the plug and/or wires may be saturated with oil. You can try swapping plug wires around, too (if they will reach), to see if the problem moves with the wire. A dead or missing cylinder can sometimes trigger the other faults/symptons, such as a perceived vacuum leak, faulty camshaft position sensor, etc.

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2009 X5 3.0
2001 X5 4.4 - Sold