Engine Light goes on. Dealership said valves need to be replaced. Cost? on 2002 Toyota Avalon

Can drive the car but engine light still stays on.
Dealership said there's a box that holds carbon and is clogged...needs to be cleaned or replaced.

Asked by for the 2002 Toyota Avalon
need more info but if there talking about your idle air control box they are correct. you can try having injection cleaned but if it fails to work your out 150.00
Thanks. Very helpful.