My understanding is that some Direct Injection engines are developing a few problems with deposits on the stems of the intake valves and right underneath the valve head as the injector spray no longer hits that area. This could be especially true on engines that use a little bit of oil and can even be true on non-DI engines.
If a problem like this is suspected one can try running a cleaner through an intake manifold vacuum port but you could get this done anywhere for much less than 400 dollars.
With the engine fully warmed up, idling, and in gear note how it idles. Heavy deposits on intake stems often cause a disruption in airflow around the valve head and this may come across as a subtle engine miss, stumble, etc.
If it idles smooth then I wouldn't even worry about it.