300tdi wont tick over

Hi, Im a new member not sure if this will be in right section.
I have a discovery 3000tdi auto 1997. when i drive then stop the engine ticks over at 1800 revs ,if i lift the pedal the engine warning light comes on, if i very gently touch the accelerator pedlal the revs come down to 850 and the light goes out , very annoying .my acelerator pedal is electronic not cable . any advise please.

Welcome to the loony zone. You need to put this in the disco section.