My 328 when I would test the disas by way of plugging them to the car without a tune and revving the engine would barely open and close, oddly enough after flashing the bimmerlabs 330i tune they behaved the same way. My valves were full of oil inside and worked fine after cleaning them. So I do wonder if the 328i stock does open and close the valves fully if they're working properly.
If you grab your disa and you shake it up and down and side to side etc next to your ear, do you hear oil slushing around? If so it's full of it inside and likely making it not work as it's supposed to. The valves should work 100% fast opening and closing fully during the inpa test, if not there's something wrong with it for sure.