1997 Tuck has difficulty starting and running in rain

[osu9400]

Any idea why my 1997 Nissan Truck rarely starts in the rain / wet weather? Once it does get started, it chugs and coughs so bad that it is not driveable.

thanks.

[574-240sx]

Check for moisture in your distributor cap. Have you done a tune lately?

[osu9400]

no tune-up recently.

if there is moisture in the cap, how do I prevent this in the future? new cap?

I wish I could find the TSBs for this model to see if something is listed.