Help re Range Rover

Have Range Rover 2.5 diesel 1997 Have just fitted cam chain ,tentioners,rails and pulleys. Vehicle is running perfect at idle and when revved stationary, but when in gear and driven goes into emergency mode.Have been told by technition that it is most likely "Engine speed signal lift sensor"
Q. What is this?where is it located?and is there any connection with this fault and the work carried out?
Await help

I think that is a reference to two items, lift sensor incorporated into No 4 injector, and sensor picking up flywheel speed. Rear of engine same side as injector pump

Many thanks Phantom 21 sounds like crank sensor!