I had a 4JH4E with similar simptoms. It started creating oil. Turns out there was an intermittent problem with the fuel injection pump. I couldn't get it figured out till well after the warranty. Make sure that you document the problem so that it can be considered a warranty issue. It cost me $2500 with me doing all of the work. It would smoke white after getting above 1800 rpm's. Not sure that is the problem with yours but worth considering.
Between us there was, as I have already said somewhere, the bond of the sea. Besides holding our hearts together through long periods of separation, it had the effect of making us tolerant of each other's yarns -- and even convictions.Heart of Darkness Joseph Conrad