I fitted a dump valve to my car about 6 months ago and it has worked fine until yesterday.what happens is, when on idle the boost sits at about 0.2 below 0 where it used to sit well below that. It still boosts fine but there is no sound from dump valve when I release or change gear now. Instead its gone back to the chatter I used to get. I had the valve off and it moves freely enough. It is leaking a little air tho when on tickover. I assume its not the dump valve coz surly it would still work when boosting and releasing. What should I check cheeRS