Plainfielder

I have been trying to figure out what this problem is for a long time now. When the engine is cold, it will start, shoot up to almost 3000rpms (sometimes just 2000) and then shoot back down to under 1000 and start shaking and knocking intill it dies out. When I give it some gas to make it stay over 1000 it'll stay running and eventually idle on its own. And when I say engine cold, not outside temp. It can be 90 degrees out, but if the engine hasn't been running for a while, it'll do it, but if it's like running into the store or something it'll start fine. Also, sometimes after I get the engine to stablize, when I put it in drive it'll do what I call "hyperactive engine" where when I accelrate the rpms with remain wherever they were for about three seconds after I take my foot off the pedal. Sometimes it's scary to the point where I put it in N so the car doesn't jump. It's like its stuck. And the last sign, it stumbles a tad when I accelrate (no matter what).

Thanks guys!
1995 Ford Mustang V6 with a BBK CAI and cut off exhaust.