Try Dawn.

 

First pull the cover off - straight up, then wash it with dish detergent as suggested above and rinse it off with water, then dry it off and reinstall it.

 

Car Care Nut on YouTube had a recent video where he recommended using Simple Green for engine compartment cleaning. I used the new Gunk Engine Wipes on my engine cover and all through the engine bay and it did excellent job and did not harm plastic or rubber.

 

recently been peaking under engine covers of all the cars in our family. there is often stuff to absorb, such as spilled oil, & stuff to vacuum such as 1/2 eaten acorns & other dried vegetable matter & rodent droppings

agreed Dawn dish soap is a reasonable suggestion. I often just wipe mine w/ whatever I have handy. generic cleaning wipe or an Armor All wipe

fwiw - this time of year I also go around all the cars & wipe all the rubber gaskets & their mating surfaces on all hoods, hatches, trunks & doors with protectant. helps keeps them from sticking. gotta do it before it gets cold tho. that stuff doesn't spread when it's below freezing

fwiw - engine covers just pop off. pull straight up. you might lift the back or the front 1st. there's usually 4 pins that fit into rubber holes under the cover

under Daughter's 2017 Corolla engine cover

wear disposable gloves

more fun & games here do not fear the engine cover

 

buy a spray bottle of gunk cleaner at walmart, or simple green...

 

I like the look of my engine cover but i took it off and hung it up on the garage wall for now, It just traps more heat and makes it hard to see things like the beginnings of oil leaks from the covers. also, I think the extra heat trapped will cause the wiring to your coils, injectors etc to deteriorate faster. As far as cleaning it, take it off and wash it with dawn dish soap. You may end up with some oil stains that will not come out just like you might get in your clothes, sometimes some of the spots just get absorbed into the paint on the cover, you could always repaint it and make it look awesome, plenty of how-to videos on youtube, proper paints to use and the like. If you have a steam cleaner like this, it makes cleaning grease and oil off anything in the engine easy, I use my steam cleaner whenever I detail my engine, steam and wipe with shop towels it comes out great and gets up and off the stubborn stuff I just can't seem to get off with scrubbing.

 

, sometimes some of the spots just get absorbed into the paint on the cover, you could always repaint it and make it look awesome, plenty of how-to videos on youtube, proper paints to use and the like.

Isn't the engine cover on the Camry made out of a spongy black foam which is not painted? The cover on the 5th generation RAV4 is unpainted flexible foam material.