What is this?
 

I bought my 4Runner and tore the motor down to rebuild it and this was stuck in one of the water passages. Can someone please tell me what it is? Thanks, Travis

Looks to me like it's some sort of protective cap for something.

Previous owner may have had the cooling system apart, and another lowly sole, dropped it in the return hose opening.

It circulated around the cooling system until it lodged where you found it.

knock sensor/oil pressure boot? On my first gen runner it is soft rubber.

the little filter on the end of the vsv on the valve cover?

Whatever it is, it doesn't belong in a water passage!

Easy one, its a "gas filter" (not gasoline either) and its located on a VSV which bolts to the valve cover. Usually, there is 2 or maybe 3 VSV's When I say "gas" I mean gaseous" as in air filter. (remember science class, ie liquids, solids and gasses)

Thanks!!! I thought that was what it was but was having a hard time figuring out how it ended up where it did and there were still three on the valva cover. I gues someone made a mistake and tried to cover it up!! Thanks again. Travis