I think mine may be duff is there any way to check this for sure?

It crackles and pops like mad on the overrun and read that this is one of the symptoms

If it is is there any way to repair it or does anyone have a working one for sale?

Thanks

 

You should be able to hear a click when u operate the throttle from under the bonnet but u have to listen very carefully

 

Thanks I will check later