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VW Jetta rough running in wet weather

My carpool partner has a 2002 Volkswagen Jetta and it has this weird tic: whenever the humidity reaches a certain level, or if it sits at the park&ride all day in the rain, its does NOT want to run. it’ll start just fine, albeit rough, and flash the engine light the entire time while we sit and wait for it to settle itself, sometimes up to 10 minutes. Sometimes it never does and she drives it while it runs rough, but it doesn’t feel like its good for the car.

My carpooler has a friend with a newer Jetta and he has reported the same problem. She has taken it in and pointed out this issue but her shop doesn’t have an answer either. what is going on with the Jetta?

Typically that means moisture in the ignition system, plug wire or distributor cap would be the first two things I would check/replace. If they are original it is time to replace them. If they are not that old, I might test them. When they are giving your some trouble, turn the engine off, and spray the wires with some WD-40, if that works replace them.

I echo Joseph . . . but I’d just go ahead and change the distributor cap . . . the plug wires . . . the spark plugs . . . and the rotor. This sounds like classic bad wires to me, but electricity will seek the easiest ground, so eliminate the possibility of the spark going anywhere but the tip of the spark plug and change all of the components. Curious . . . how many miles on this 6 year old Jetta? Rocketman