Sputters and rough idle when there is heavy condensation or wet weather

Actually, this is usually a really simple and cheap (sometimes free) thing to fix. On just about any vehicle with a distributor, moisture can start getting in under the cap and cause the rough idle that you are experiencing. What you need to do is pull off the distributor cap (pictured below) by first labeling and then unhooking all of the plug wires from the cap. Be sure to label the wires and where they go, otherwise you will have a great time figuring out what goes where. Then you will unscrew the two screws that hold the cap down. Then all you have to do is inspect the cap (closely) for hairline cracks and also look at the seal for any cracks or general stiffness. Also look at the contact points inside the cap for corrosion (greenish white-ish crud) and, if it has rained recently, moisture. If your problem is simply dirty corroded contacts, clean them up with some sand paper and put it back together. If you have got moisture under there, then replace the cap and gasket/seal.