yep, you should be able to cap it off but i would try to leave it as a reversible method of plugging it off.

i wonder why the butterfly wasn't used in comparison to the sleeves on all models, it seems it would have been a lot less problematic.

oops double post..

true that. there is a thread on it so i should just try to find a nut with a closed head to seal it off. you never know eh?

i wondered the same thing. the sleeves on the usdm versions seem to have so much metal to metal surface area when installed in the ports its no wonder that most of them rust in place when left unused for a while. also the fact that the butterflies are always open seems better than being shut in case they stopped functioning it would be much less of an annoyance in comparison.

so if I wanted to keep them working on a s4 will I need the vaccum spider, air control valve, and airpump?

if you want it to work properly, yes. otherwise you could use the exhaust backpressure if you tune it to open when you want them. downside to using exhaust gas is it isn't very easy on the passages and diaphragms that it will be controlling.