Does anyone know the purpose of the under engine black plastice cover? I lost mine this past winter driving in the snow. I havent missed it, and perhaps it is running better (cooler engine area?)
By the way--2007 with 131,000 miles and still running great.

 

for one, it protects the motor from debris that could come up from the road and possibly do damage.... and two, it ties the bumper to the underside of the car, stiffening the bottom of the bumper

 

Might also smooth the airflow and even reduce drag a bit.