Check the ignition coils...especially at the spark plug wire connections.

I know it's a stretch, but my old VW had the same problems whenever the environment was moist...I finally traced the problem to the ignition coil...corrosion was discovered at the main plug lead.

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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