Plugs and wires should be done every 60K. How many miles do you have?
Do the basic cheap stuff first, new air filter, clean the throttle body and IACV valve, replace plugs. You need a new MAF, do those easy items and see how it goes.
I would replace the plug wires next.
Also double check all the air hoses, I know you said they were checked, but double check everything and make sure they are air tight.

 

There are 95500 miles on the Rover.

What is the IACV? What plugs/wires do you recommend?

Thanks again for all your help. You have no idea how much I appreciate it.

 

I don't want to change the subject, but how hard is it to change the head gaskets? It seems they are worn out and are letting oil leak out. The engine runs hot and smells of burnt oil.

It hasn't happened for a while, but every so often the anti-freeze just evaporates and it starts to overheat. I fill up the reservoir and it's fine. There are never any traces of leaking anti-freeze on the ground.