Welcome to JA.
What year, model and engine size is this Rover?
You are saying it revs up when first started or does it do this all the time?
Is the check engine light on if so do you know the fault codes stored?
Let me know so I can help you. Thanks Daniel
Sorry I sent that first response as an answer not an info request. Just to clarify it only idles high right at start up? How high does it idle up? Does it idle high any other time?
Discovery 1 or 2?
Not meaning to ask all the questions I just need a little more info. Let me know. Thanks
Im sorry you had to leave me negative feedback for me accidentally sending the response as an answer instead of an info request.
What I would do is first clean the throttle body becasue it could be sticking and causing the high idle. Then I would make sure that the throttle cable isnt adjusted too tight. I am not sure if you have a series 1 or 2. But if it is a series 1 I would set the base idle. Technically you will have to hook it up to the LR diagnostic equipment to adjust it but you can do it by ear. Look at the top of the throttle body and you will see a little circular cap drill a hole in it and screw a screw in the hole that fits and use a pair of pliers to pull on the screw to pull the cap out. Using the right size allen adjust the idle screw adjust it to about 700 rpm. If it is a series 2 then you cant adjust the idle. On either one you will need to check for vaccum leaks use carb cleaner and spray down the hose and gaskets an if you hear it rev a little then that is where your leak is at. You issue could be either one of those things. Let me know what you find.
I am getting off line now if you need anything else respond and I will get back to you first thing in the morning. Thanks