dump valve failure

ive noticed my dump valve no longer makes a psssh sound it just chatters, even under heavy load, could this be knackered? if so could it cause hesitation when accelerating and low power but still same boost? my hesitation issue has started again so i switched out my maf for my old one (which i thought was also knackered) and at the same time i adjusted the apexi dv (turned the aduster to make the hole smaller), the issue sort of felt better and was boosting alot better but just chatters.

When i had the car into protuner he done a boost leak test and fixed a few boost leaks but he said the dump valve was also leaking slightly. now the car is pretty much undrivable with serious hesitation/fuel surging at low revs and light throttle and jerks at certain points before accelerating properly, sometimes when pulling to junctions the car has a couple of times cut out.

im hoping it could either be an o2 sensor or dump valve issue? however the car idles perfectly

any advice?

Can you not block the dump valve off altogether then try it see if that makes a difference .... the o2 sensor iirc you can ohm test it theres a thread on here i think about doing it ....

Blocking off the dump valve is a good idea. If there is no other boost leaks try that first, always easier to eliminate one thing at a time

ok ill try blocking it off, do i just plug both the hoses?

What you got sye a recirc ?

no ive got an apexi, does look pretty old and tired

http://www.mymr2.pwp.blueyonder.co.uk/pics/BOV/pic1_big.jpg

i just turned the red bit around to the smallest hole

If the car cuts out when coming up to a junction yet idles properly if you Rev it then let the revs drop at stand still there is another culprit it could be
That being the brake servo or one way valve going to it is leaking.
So in other words when you hit the brakes to stop at a junction or what ever you are losing vacuum pressure which is enough to make the revs drop momentarily enough for the engine to stall