It is very unlikely you caused the problem by washing the engine. If that was the case, every car like yours would be sitting on the side of the road if it's raining. You also would have noticed the problem right away, not after the residual water had two days to evaporate.
White smoke from the exhaust is a sign of engine coolant burning in the engine due to a leaking cylinder head gasket. You'll see the coolant level dropping in the reservoir too. There's two ways to verify this. Your mechanic can do a chemical test at the radiator or reservoir, or you can add a small bottle of dark purple dye to the coolant, then check a few days later with a black light. The dye will show up as a bright yellow stain. If the cylinder head gasket is leaking, the dye will be found inside the tail pipe. Auto parts stores have the dye, and many of them rent or borrow tools. If they do, they are likely to have a black light for this purpose.
When the Check Engine light turns on, there will be a diagnostic fault code related to something that could adversely affect emissions. A misfire will do that by allowing unburned fuel to enter the exhaust, and the code is almost surely going to be related to that misfire. On a '96 and newer car, the fault code will even specify which cylinder is misfiring. You can check that spark plug wire to see if the water allowed it to start arcing at the spark plug. That will leave a carbon track behind that conducts the spark away from the spark plug. It is best to just replace the plugs and wires for that. Cleaning them rarely works because that carbon will be burned into the rubber boot.
The misfire could be caused by the head gasket too but remember that air and fuel are still going into each cylinder. The coolant that's sneaking in would have to extinguish the spark, otherwise that fuel would still ignite and there wouldn't be that misfire. You may have two issues going on. If the cylinder head gasket needs to be replaced, that would be the time to have new spark plugs and wires installed.
Tuesday, October 8th, 2013 AT 11:37 PM