Thanks for your interest in Berryman.  You can use Intake Valve & Combustion Chamber Cleaner (part #2611) as often as you need to.  I know that’s a non-answer, but it depends on a lot of factors.  If you have a GDI vehicle that’s prone to intake valve buildup, you might want to run the product every 5-10k miles.  If you have a PFI or TBI engine that is less prone to intake valve buildup, then you can probably wait for 12-15k miles.