Car shudders in wet weather

I have a '96 Aurora that I have been having an issue with lately. Every time there is a bad rain storm or I drive through standing water, the car starts acting up. The check engine light comes on and starts flashing. It starts chugging, misfiring and I can't get any acceleration out of it. After a few days of dry weather it seems to go back to normal. I changed the plugs, wires, coil packs, and all 4 o2 sensors with no luck. Cannot figure out what it could be. Please Help!