Does anybody know if changing the screw on the back to alter the noise will screw up my cars idle? (sunny gti-r)
Cheers

jamin,
it may do. If you undo the screw too far out, the valve will leak when you leave go of the throttle at medium to high revs and you can end up stalling the engine because it is sucking air in through the dump valve and this doesn't pass the airflow meter and so it doesn't provide the fuel.
The usual fix for this is to tighten the screw so that this doesn't happen and also to let the car coast 'in-gear' and drop below 3,000 rpm before dipping the clutch and idling.

Andy

OK thanks