I'd like to clean under the hood of my car but I'm worried about the CPU and if there's anything I could damage with the water.

And what do I do about the short air intake? Remove it temporarily and plug the hole?

 

All-
This is what I do. I found that at the do it yourself car washes, most have a pre-cleaner. Select that option. Then without depressing the trigger,(thats the trick) you'll be able to control very easily the amount of water that flows automatically.Just keep it away from electronics. Also treat the rinse cycle the same way. Start vehicle right away when done.

 

Step 1: crank car and let it get warm (not hot or full running temp!) turn it off.
Step 2: take plastic grocery bags and cover the alternator, distributor, short ram filter and fuse box.
Step3: lightly spray down the entire engine bay and underside of the hood with water from the hose (spray nozzle is important)
Step4: liberally spray the entire engine bay and hood with Simple Green degreaser. Let this sit for a few minutes.
Step 5: With a decent jet of water, rinse the entire engine off. Remove the plastic bags and start the car. Let it run until most of the engine is dry
Step 6: you can use the simple green and a towel to get any tough stained places that were missed. Also use another towel to soak up any pooled up water places.
Step 7: This is optional, but you can now wipe down the entire bay with Meguiers Vinyl and rubber dressing for that brand new look.

Hope this helps