Something just like this happened to me on a recent trip in a 2WD Westy.  I
hit an incredible thunderstorm cell in central Oklahoma.  I can only
compare it to driving under a waterfall.  Visibility instantly dropped to
zero, and I pulled off the road more by feel than by sight.  It lasted 15
or 20 minutes, then passed.  The van started right up, ran perfectly for
about a minute, then began to lose power and died, thick smoke suggesting
too rich.  This repeated several times- each time I shut off the engine, it
would instantly restart and run perfectly for a minute, then cough and die
again.  After several repetitions (maybe 15-20 min.) it finally ran OK and
ran perfectly for the rest of the trip, which included quite a bit more
rain.  Some water must have gotten somewhere it's not supposed to during
the deluge, then eventually cleared. 

Bill
www.geocities.com/yosemite/gorge/1706