I recently picked up a 2004 C4S w/X51 and an after-market air intake system. After going through a drive-through car wash (with the car on), the check engine light came on for about 10 seconds following my exit AND there was a loud whistling noise coming from the engine bay. I noticed that there was a large amount of water vapor coming throught the grills above the engine. I figured the noise the just the water burning off the engine and whistling through the grills. But that wouldn't explain the check engine light or the general volume of the sound (which, besides whistling, sounded like a had a blow belt or something).
My after-market intake doesn't have a cover on it and I am starting to think water is getting into the engine via the air intake. The whistling and other, less describable noises go away after about 30 seconds and the car drives as if nothing happened.
Has anyone experienced this before? I am sure it is not normal and I am considering swapping to a different air intake that is covered (or for which this doesn't occur).