my 1998 Honda Civic runs well except for after it rains, then it won't run at all for 2 or 3 days until it dries out, any ideas what the problem could be?

txgreasemonkey

Wet Starting Problems

. Spark Plug Wires. Insulating rubber can begin to breakdown around 6 years, allowing moisture to seep into microscopic cracks in the rubber and provide a leak path for the current, prior to reaching the plugs. Electricity finds the shortest path to ground and moisture can allow secondary or high tension voltage to discharge somewhere besides the plugs. It's a good idea to clean and spray spark plug wires and boots with silicone, which is a dielectric and will also help seal and protect the rubber from ozone. Problems involving old wires normally show up in wet or humid weather.

Here's how to diagnose problems. On a dry day, warm engine up to normal operating temperature and spray spark plug wires with water from a spray bottle. Note any changes in engine rpm. If idle speed drops, the wires are bad. On a wet day, in which the car won't start or starts hard, dry the wires with a paper towel and spray with WD-40, which displaces moisture. If the car starts, the wires are bad and should be replaced.

. Distributor Cap. Moisture can develop inside the distributor cap. Make sure to use a ventilated cap with a good O-ring. It's important for the O-ring to seal properly between the cap and housing. Coat the O-ring with silicone grease. If moisture has developed, dry the inside of the cap with a paper towel and spray with WD-40, wiping off the excess.

. Dielectric Compound. An excellent product to have on hand is Motorcraft Silicone Brake Caliper Grease and Dielectric Compound (XG-3-A). It's available at your local Ford or Lincoln/Mercury dealer. It's amazing the number of applications this product can be used for; e.g., lubricating O-rings, rubber gaskets, disk brake caliper pins, plus using it as a dielectric compound for weatherizing battery and starter terminals and cables, main grounds, main ECM ground, ECM connectors, igniters, coils, spark plug connectors, coating spark plug porcelein, and tail and brake lights. Obviously, this product helps prevent wet starting problems in seemingly small, but significant, ways. Attention to detail makes a big difference when operating in wet, humid conditions--especially around salt air.

Pay particular attention to the above section about the distributor cap. If I were you, I would replace the distributor cap and ensure the O-ring makes a good seal.