How often do you change engine air filter on 2006 toyota solara?

When it's dirty.

The replacement schedule listed in the owner's manual mandates replacement every 30,000 miles and only visual checks every 5000 miles or six months whichever comes first. Replacement can vary greatly though depending on driving conditions. In dusty environments, replacement might be necessary far sooner than 30,000 miles.

The replacement time is the same for your cabin air filter. Replacement instructions for that are in your owner's manual.

Cheers