How much does it cost to remove the carbon build up in the intake valves?

The cost will be removal in installation of the intake manifold, replacement of the intake manifold gasket, and the cleaning will more than likely be the shops hourly rate. Likely that one of the certified shops here will be much more affordable than the dealership: http://repairpal.com/mazda-within-10-miles-of-stafford-texas-77477

We have a new chemical process to clean the valves on direct injection engines, please give us a call at Christian brothers Automotive North Katy, 281-578-7799. This process is not invasive and 100% guaranteed. No need to remove intake manifold.