Paws

I have a 2008 Cobalt LS 2.2L 4Cyl. I took off the engine cover to clean it, (I was also a little curious to see if it looked better without the cover) and I noticed it has dust and spots all over it. I didn't touch anything except the engine cover, as I didn't know what I was doing. How do I clean this without removing it? Also, the brown pieces that look like mouse droppings on the valve cover, is foam that had flaked off the engine cover. (Just another reason to be without it.)