Took the air filter cover off to inspect the air filter (hoping to improve mileage) the air filter was filthy! The filter in the cover looked dirty, but going through forums turns out it is activated charcoal, so should be fine. But, when I pulled the air filter out I found that there were a lot of seed shells inside! They are all the same, maybe safflower, but how in the world could they even get inside?
Most likely a mouse/rat/squirrel/etc is entering a section of the intake plumbing, BEFORE, the the air filter. Perhaps the creature was using the snorkel box as a storage for all of its' seeds. As you drive, the seeds get sucked-up, but stopped at the air filter. You will probably have to put a mesh screen (hardware cloth, small square .25in x .25in) around the opening to block the creature(s). See this link to see the picture of the snorkel and the opening, the creature(s) most likely entering from. What is this black plastic thing under the hood? | PriusChat
You have mice. Very very common in a lot of modern cars. They like the air filter nice and warm overnight. Pull the interior cabin filter next they have built a little Days Inn in there. So you do not garage the car. They cause a lot of damage as they are very attracted to chewing on the soy based wiring and have destroyed many a harness on this site. Use the search forum button up top and search Mice There’s lots of threads about it here.
I put a 1/4" spacing galvanized steel wire mesh over the intake snorkel entrance. Same thing for the cabin air intake. The latter's a bit involved, have to take the wipers and cowl off.