clutch in, engine stalls

Well when im driving down the road and i go to slow down, when i put the clutch in the RPMs drop real low and then come back up to around 1200. Sometimes, if the clutch is pressed in around 3000 or higher, the RPMs will drop and the car will just stall. It starts right back up, but this is a big issue! any ideas?

BTW, this is a b18c swap in a 94 civic.