My 2019 LDV T60 is running rough when turning the steering wheel

This vehicle is one of the few (thanks to the age of the basic design) to have stuck with conventional hydraulic power steering versus the newer, more efficient electric power steering systems now available. As such, the power steering in the T60 is driven by a belt turned by the engine.

When you apply full lock to the steering, this loads the pump sufficiently to actually slow the engine down. When that happens, the engine’s vibration frequency changes and your ears hear that as a rumble or vibration.

This could be because the pump or something else inside the system is worn and contributing a greater load to the engine, or the belt is out of adjustment or alignment. Perhaps you simply have too little air pressure in the front tyres which is loading the system up when you turn the wheel. Beyond that, a small adjustment to the engine’s idle speed should stop this occurring.