My KA stalls...

[devildr1ver]

Sup fellas. Uh, I don't really know what to classify this as so I had a hard time searching for this but my KA stalls a bunch. I don't know why, I don't know how...but it does. First, I start it up. It will idle for a bit at a little under 1k rpms and then just drop dead. I just recently bought the car from some guy and the whole thing seems like I've already fixed most of everything that was wrong with it. I still got an exhaust leak though. Do you guys think that maybe that might have something to do with it??? I've also heard that it could be the air/fuel ratio mixing problem or a bad fuel injector. I don't really know cuz this is my first car where I've had to really work on the engine like this. What do you think is the problem? Will it cost me a lot? How do I fix this? Idk, somebody help...please. Thanks!