On my 06 997, I open the engine cover as I am drying the car. I've noticed water drains from the lid directly into the air intake, so I'm careful to cover it witha towel immediately upon opening. It doesn't appear to get wet during washing, only after it's opened. I open it to drain water from the "wing", otherwise ,you'll have water streaks coming off both rear corners of the car. Washing your car with the wing in the up position might give the H2O a means of entry into the intake.
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2006 997 carrera coupe