Good car. Yes, follow what I described but that intake manifold is internally shaped with the long runners curling around it is near impossible to get a boroscope into a runner and to the valves. So removing the IM is the best. Do not be alarmed at the deposits unless they are more than twice the original size of the valve, they are not hard to clean on these as the intake manifold is in the front of the engine. Then with the IM removed you can look into the ports and there will be 2 intake valves per port. Pick one that the valves are fully open, or turn engine over until one is. Then with a needle nose pliers you can grab a valve and "wiggle" it. It should barely have any deflection side to side. If it seems excessive then at higher RPM's the valves are unstable and would need head removed and old guides pressed out and new ones installed.
Be aware all GDI engines will have this coking pretty severe. Mazda, like all the newer GDI engines has this issue on the pretty severe side, but it is a great engine design.
So to summarize, if you do not have the opportunity to remove the IM, just drive the car and look for misfire codes, etc. You know from your F body when an engine is running well. Make sure to check oil level before you start it also. If it runs/rides/drives good then just deal with the manual intake valve cleaning after the purchase. If you need step by step instructions, I will be happy to provide them.
GDI Tech
