The other day I opened up the hood while it was raining, which sent a sheet of water down on the firewall. A few miles later, the engine died. Radio and dash lights stayed on and the car started right up again. This has been happening for three days now, averaging every 5 miles or so. If I'm going above 30 mph sometimes it will re-start itself (automatic trans), otherwise I can switch the ignition off, then re-start it while coasting. Yesterday was dry but it happened anyway. Kind of hairy when the power steering suddenly stops.

Looked inside the fuse compartment and don't see any moisture there. This problem seems to affect the engine only, not the electrical accessories. Any ideas or tests I can make? These random things can be expensive to trace and hard to reproduce, so I'm hoping someone can help me narrow it down.