Direct injection is why the ND's engine is efficient, and it is also why you have to think about the intake valves. On a port-injected engine, fuel washes the back of the intake valves; on a DI engine like the PE-VPS, it doesn't, so oil vapor and combustion residue can bake onto the valves as carbon over many miles.
This is a long-term, high-mileage consideration, not a first-year problem. Symptoms, if they ever appear, are gradual: slightly rougher cold idle and small drivability changes over the years.
How to manage it sensibly:
- Change oil on time with the right grade. The ND specifies 0W-20. Fresh oil and a healthy PCV system reduce the vapor that feeds valve carbon.
- A catch can is the common enthusiast preventive; it traps oil vapor before it reaches the intake tract. It's optional, not mandatory.
- Occasional Italian tune-ups help. This engine likes to be revved; regular full-throttle runs keep things cleaner than a life of gentle short trips.
- If carbon ever becomes real at very high mileage, a walnut-shell blasting of the intake valves is the direct fix.
On spark plugs, follow the maintenance schedule and use the specified plug. High-compression DI engines are fussier about plug condition than old low-compression fours, so don't stretch the interval to save a few dollars.
None of this is alarming. It is simply the maintenance profile of a modern direct-injection engine: right oil, on time, rev it out, and check the plugs when the book says to.