Where is the cabin air filter on a 99 s10 4.3L?

SOURCE: Cabin Air Filter Location

Empty glove box, remove axcess panel and the open the axcess door, two (2) filters inside,

SOURCE: Cabin Air Filter

good news is it can be changed with no tools in about 2 minutes. just take out the glove box and the cover comes off easy.

SOURCE: cabin Air Filter

Open the glove box

Remove all of the contents in the glove box

On the right side, dis-engage the rod going to the split plastic pin on the glove box door

Squeeze both other sides of the glove box to defeat the stops that keeps the glove box from falling open

Observe the box in the area vacated by letting the glove box drop down, this is the heater box

Locate a rectangular cover (approx 7 " x 2"), it is located on the face of the box; facing you.

Pull this cover out towards you, the cabin air filter is located in the tray that is connected to this rectangular cover.

This should help you replace it.

SOURCE: LOCATE AC CABIN AIR FILTER

no cabin filter on 2003 crown vic cabin filter is under pass cowl trim

SOURCE: 2002 Toyota Sienna cabin air filter??

Unfortunately, no.
Toyota began installing the cabin air filters in the Sienna product starting in 2003.