Okay, I have a Hyundai Accent 2000.
I was just experiencing the same issue.
My car would run fine, for about 10 mins. As soon as it warmed up, it would start to miss fire and eventually stall. Mind you, all of this happened very quickly, i'm talking within seconds.
Once the car had stalled, i lost everythign. It was a heavy bugger to push with no power steering let me tell you
In short, the issue was the Crank Angle Sensor.
You'll be able to find the crank sensor in the side of the engine block, behind and below the exhaust manifold, near the transmission. It's held in place by one 10mm bolt.
I had lube mobile come out and replace this for me as i had no car to get to the store to do it myself. Cost me $150 all together.
Now, the car starts and runs well.
The mechanic did warn me however, that the Crank Angle Sensor and the Cam Sensor pretty much work in conjunction. So if one goes, then the other one may be on it's way out too. I am yet to get this replaced, but the car is running fine for the moment.
Hope that helps out