I used to work at toyota 5S dealership. There, i used to clean throttle body every 10000 kms. Other then that, on CNG cars, it gets clogged every 5000 kms so I always cleaned it properly at 5000 kms. CNG installed engine gets more carbon deposits in the throttle and IAC valve is almost chocked. the rpm are running up and down mostly.
It scares the normal road side mechanics to open a throttle body and clean it. even i ave seen people working in Honda and toyota dealerships who are scared of opening the throttle body. they just get rid of it by spraying some carb cleaner. the inside of an IAC valve is properly cleaned by removing it out from the throttle. cleaning its inside and then lubricating with a few drops of oil.
PS> There is no harm in opening a throttle body and cleaning it properly even at 5000 kms as far as you know how to get the job done