Lower engine compartment cover.
 

New guy here with 2008, 2.4 liter, 24,000 miles purchased used at 21,000. Changing oil today and removed lower engine compartment cover--what a pain. Bust two of the plastic push clips. Any reason why I cannot just leave that off or does it need to be in place for airflow purposes or corrosion control. If it is just corrosion control I really don't care because this car will be gone by 60,000 or 80,000 miles. For me that is 2 or 3 years. If it is airflow then I will probably deal with it and put it back in place.

You can probably find replacement push pins at any auto parts store for a couple of bucks. If you know how to work them they shouldn't break.