Volvo 460 does not start when raining

Hi all
The car is a 460, 2.0 liter automatic, first registered in July 1996. Only
about 140.000 kms. About a month ago, the wife drove into a large pool of
water on the road and the car died. Since then, we've had various
difficulties, but only in or after a heavy rain!
What I have done: Replaced all the high tension wires, spark plugs,
distributor and rotor arm (they were due anyway). Poured stuff in the fuel
tank to get rid off condensation, and measured the engine sensors easily
accessible.
The car is fine when allowed to spend the night in the garage, but that's
not always possible. Car wouldn't start in the wet air this morning. Used
the Data Link Connector to read error codes, but all I got was 1 1 1, which
is No Fault Found.
Going out to test the fuel pump, although it's probably a long shot. I'd be
grateful for any other ideas, before the wife completely loses faith in my
mechanical skills ;-)

Regards

Ivar Petur

Hmmm. Maybe check the coil? When I've had this problem it was aging
insulation on the spark plug wires and coil wires, allowing the wires to
ground to the engine block right through the insulation.