Hard to determine without being there, but do you know if the engine wiring harness has ever been replaced? The factory wiring insulation (designed to deteriorate in order to be landfill-friendly) deteriorated far sooner than engineered, exposing bare wire to adjacent wires, creating short circuits that manifest in a variety of ways...including misfires.

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car