After using the upper end cleaner (mentioned in the video I posted earlier) in each cylinder, my idle smoothed out a lot and I don't feel a distinct misfire anymore. It's not perfect, but the X5 has 170K. Also, it hasn't thrown a code since the cleaner. I think I might do the cleaning process again, and see if things improve even more, but it appears my code/misfire problem is solved. If it returns, I'll be sure to update this thread.

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Current:
2003 X5 3.0 -- 170K
1996 Z3 1.9 -- 128K
1968 Ford F250 Camper Special

Previous:
1994 BMW 318is
2004 325i
2003 Honda Accord
1969 Ford Bronco
1963 VW Manx 1776cc1969 VW Bug 1600cc
1963 1/2 Ford Falcon Sprint 5.0
1968 Ford Mustang
1964 Ford Falcon Futura
1964 Ford Falcon Ranchero
1962 Ford Falcon
1953 Chevy Sedan
1994 Jeep Wrangler