I own a 2015 Mazda 6 (original owner) and I have heard that due to direct injection that carbon can build up on the intake valves and cause problems. I have a bore camera which I can place inside the cylinder but this will not give me a view of the intake valves which are known to carbon up on the intake side. Is there any way to get a view of the intake valves on the intake side without removing the intake manifold?

 

Run the borescope down the intake manifold runners, if you can negotiate the corner(s). Otherwise, no, you'll have to take off the manifold.

 

Could you elaborate on what an "intake manifold runner" looks like?