Zeet

I have a 2000 SE NB with a Jackson Racing Supercharger M45(I think). When stopping, the car would stay at 1500 for few seconds then drop to normal idle. Sometimes it would get stuck at 1300 while stopped. While standing still, kicking throttle up after it was normal idle, it would stop at 1500+- for 5-15 seconds, then go back to normal idle. I switched the IAC valve with a spare i had laying around, same issues.
Rescently I have rerouted my IAC valve hose. Used to have a 4foot hose running to the intake pipe. I blocked off the port at intake. Installed a small air filter on IAC with a oneway valve(Which was already there prior to this adjustment).
Now when it's started, it dies off instantly. I can hold throttle open, idle it at 2k-ish until it warms up, then it runs good.
I confirmed the oneway valve is positioned correctly. Also I hooked up my spare IAC valve (not installed) just to see if it opens when ignition is on ON, the valve didnt budge.(Not sure if thats a valid test.)

Any suggestion on what else to try? Has anyone ran into this problem on a SC'd miata?