Engine races when idling

Hi. I have a very unusual problem with a Landrover 110 (2.5 turbo diesel), and hope that someone may know what is going on. After the engine has been idling for 10-15 minutes, on touching the accelerator just slightly, the engine races to well above full throttle RPM -ie.screaming revolutions - for about 5-10 seconds before dying back to idle speed. Advice from mechanics suggested oil-carry-over from the engine breather into the air intake before the filter,  causing the engine to run-on from directly ingested oil. But disconnecting the breather pipe has failed to stop this happening, and every 6 months or so it happens aqgain. This is very disconcerting, and you feel as though the engine is about to disintegrate! The engine has done 135,000 miles without rebuild, but uses very little oil even after a 500 mile trip. It does not appear particularly worn, there is very little blowing-out of oil from the breather pipe to speak off, but power has dropped off about 10-20%, possibly we think from a worn turbocharger. Does anyone have ANY ideas at all what could be causing this? MANY THANKS.

Could this be a result of oil from an oil leak to the turbo-charger bearings being sucked into the engine and burnt as soon as you touch the accelerator, as air flow into the engine increases?