Originally Posted by montreal red
This the very reason why I ditched my N54. This engine will not be a long lasting one. There isn't any defined maintenance for this, but if I was tracking my car, I would be cleaning the intake ports and valves once a year. Regular driving every 2 or three years. It's a bit of a bitch due to the some electrical components that are in the way when you try to gain access to the intake manifold. I tried and gave up, sold the car and bought a truck.