The only issue I have ever had with spraying the engine bay down, was on my Talon. I sprayed the engine bay down and then just let the car sit. The next morning I went to go to Fontana and the car was mis firing all over the place. There was water in the spark plug wells causing the mis fire. I went and cleaned as much of the water as I can out of the wells and then drove it around until the rest of the water evaporated out. So after you spray it off, drive the car until the engine is dry.

 

Wow this thread really sparked some discussion. Anywho after about 2 hours of letting my car sit from last drive I covered up the filter, any important looking electrical and plugs with plastic market bags. Then spray on some de-greaser in areas where needed, let it sit for a few mins and then gave the bay a quick spray down where needed, never focusing on one area for longer than 5 secs. All went smooth and bay looks a lot cleaner.

On a side not, do not spray de-greaser on aluminum for to long as it stains the finish. The piping on my UICP looks all spotty now lol.