I've had an intermittent miss for several weeks. No codes. Had done all the basic troubleshooting stuff but hard to find something when it isn't happening. Recently it started missing more frequently but still no codes. Used software to monitor engine but didn't see anything conclusive though with cutouts open it became clear it was only on one bank. I had already check for vacuum leak with propane and brake cleaner but found nothing. I had another MAF so swapped that out and it made no difference. Didn't seem like it was a plug issues so I decided rather than check them I would make a smoke test machine and check for vacuum leak again. It was easy to see the vacuum leak with smoke tester. One of those never should happen things. One of the valve cover bolts had backed off. I tightened the bolt and vacuum leak is gone.

It ran terrible at first, stalling and even went into engine failsafe a couple of times. Took about half an hour for engine to figure out leak was gone and make the adjustments. Held RPMs at 3000 twice for a couple minutes. Let it idle for ten minutes with air on. Let it idle for 10 minutes with air off. Revved it several times to different RPMs and let it free fall to idle. Runs fine now.

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