What on earth is this sensor and what does it do? I've never seen anything like it and there appears to be 3 vacuum-sized lines that are all disconnected.

My Rover is a early 1994 Discovery with Lucas injection.

 

?? wtf....lol never saw one of those....my '95 does'nt have it

 

That looks to be where the fuel cut off switch would normally be.

 

I think it's a vacuum switch that operate the coolant bypass valve for when you put the AC on with recirculation on, the coolant won't go in the heater core, so you'll have cooler air.

 

Correct. Only 94 and very early 95s had it. The activation switched are on the back of the temperature *****