[curtis73]

Many things can cause misfires, including MAF/MAP, low compression in that cylinder, O2 sensors, cats, you name it. The computer registers something about a misfire and it probably just picked it up in cylinder four.

Given the fact that it just rained, have the code cleared and drive it. If it comes back, have it re-read. If it doesn't come back, it was probably just water in the ignition somewhere. You can help this by putting a little dielectric grease in the boots of the wires (both ends) and making sure the rest of the ignition system is in top condition. Just 'cause its new doesn't mean its right.