This is getting better actually.
If the mixture had been made rich by the fuel trims being altered, then they could go rich.
This could be an airleak relating to a crankcase ventillation pipes or valves. PCV valves are designed to control the airflow through the crankcase.
If the pipe is cracked badly, or the valve is sticking, the expected level of ventillation will not be achieved.
With crankcase ventillation systems, many are designed to bypass the throttle body/throttle valve, which could act as a significant airleak making the engine run leaner than normal, especially if the rubber pipe is leaking.
It depends where the crankcase inlet is positioned with respect to the airflow meter.
If the inlet is before the airflow meter, then the airflow meter won't know anything about it, but if it is after the airflow meter, then it should be compensated for very easily, but if the fuel map is based around the throttle position sensor data, it might start to change the data at each throttle position data point.
Of course I am not familiar with all of this ECU map stuff on the LR system, but I am sure that there are some who could fill in the relevant gaps and tell us what the system would do.
