I have a 1996 TDI 300 disco. It has a problem while driving. As it is driving along at low speed ( not under power ) the engine drops to idle, ( about 750rpm), and then the "check engine" light comes on. When I push the gas peddle it comes back to life.
I have had the diesel timing tuned, and the potentiometer replaced as it come up as a fault on an system scan.
I picked it up a couple of days ago, and the problem still occurs.

 

Sounds like a throttle position sensor, if it has one.
We dont have diesels here in the US so we cant help much.
This definitely sounds like a electrical issue.

 

I'd take it to get it checked out. There are enough things it could be that you could just be shooting in the dark replacing parts.

 

The sad thing is all of that work was done by a specialist landrover mechanic who has 30 years experience. He suggested I try the internet as it has him beat. It has a 'drive by wire' throttle system apparently, and that is why he tried replacing the potentiometer.

Thanks for your suggestions, keep 'em coming.

 

There are a fair number of 300Tdi's in the US but they are all conversions, and people generally use earlier version that don't have the electronics. That's what I did as well.
By "potentiometer" do you mean the throttle position sensor on the pedal box? Because that has a backup idle switch that the system defaults to in the event sensor failure, and your symptoms sound like it's defaulting to that.
You might try this forum in the UK, Land Rover UK Forums
Be sure to come back and let us know what the solution is.