General Whats this stupid thing for???

[MazCinq]

Ok, so since I bought my MW a few months back I have always thought on idle its abit loud but just put it down to it being diesel and im used to petrol.


But, when playing around with stuff before, I found that pushing the plunger down on the item pictured made the engine run loads quieter and smoother on idle, to the point of what I was expecting from a smoker.


My questions are,


What is it???
What does it do???
On idle is it meant to be up or down???? Up Noisey, Down Quiet.
Do I need to replace something????

 

[Davren]

It's a vacuum diaphragm that operates the idle shut off butterfly valve.

Whenever the ignition is switched on, the butterfly valve should be full open. When the ignition is switched off, the valve should fully close to prevent the engine running on.
.

 

[MazCinq]

Ahhh ok, kind of like a throttle body on a petrol but it's to prevent runaway, ok as long as it's working right lol.

I will keep looking for the reason why my engine seems loud.