tads
Do the vacuum lines first. Several vacuum lines missing is a lot. You Airframe and Powerplant mechanic friend is on the right track. With those missing, the idlling stepper motor will be chasing after its own tail.
Ed

 

Idle Air Control Valve? Stepper Motor? Could you explain what this is?

 

The stepper motor (or Idle Air Control Valve) controls the amount of air that goes into the engine when it is at idle. In Rovers, they are known get dirty and usually just need a cleaning.

If you are looking at the engine from the front of the vehicle, it is located just to the right of the throttle body along the air intake. It is held on by two small bolts and has a plug with three wires gong to it. It is very easy to remove. I would also clean the intake while I was at it.