99 Volks wagon Cabrio
Have you checked all your plugs and wires to be sure they are on tight. I had this issue once and it was a loose wire that was getting fire but loose enough to get wet when it rained. A cracked distributor will also cause the problem.
i have a 2002 cabrio wich had the same issue mine ended up being the ignition coil had a hair linr crack where it meets the fire wall it ran fine when dry but as soon as any moisture got in there it would not start take a small spray bottle go in a dark garage and spray the coil, cap,rotor, and plug wires look for any arcing
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