Power loss in foul weather

[Peter Sebestyen]

Baffling problem:  I have a '91 200 Wagon, purchased in 2000.  The car is
solid and strong in most conditions however when there is standing water or
slushy conditions, it loses power, gets a real throaty sound and vibration
(follows RPM's) and seems to lose some power.  It doesn't lose all power but
it is compromised.

I've run this past several people and gotten lots of funny looks and
insinuations that I smoke/drink/etc too much.  My girlfriend has been privy
to it so I know I'm not imagining things.  My assumption is that water is
getting aspirated somewhere or that something is warping.  It's difficult to
trouble shoot when it's happening because I'm usually on the road and it's .
. . raining.  I pulled the air filter (K&N) and checked for water and found
nothing and there are no visible cracks downstream from the air filter.
Further, the engine compartment stays mostly dry in inclement weather.

Has anybody experienced anything similar?  Any recommendations on where to
look or how to diagnose before the snow flies?

Thanks -
Peter