I have a similar problem, adding that it now shakes when idle...but only after a few minutes of driving. It actually now started to turn off while @ slow speeds. A former Hyundai mechanic suggected replacing the Throttle Position Sensor ($50), I will try tomorrow and let you know.
Update:
Well I had a mechanic neighboor look @ it. Said my coils were bad. I replaced them, but the car idled a little rougher. I replaced the Wireset also, idled smoother and I thought all was good. Until 1 day it wouldn't start. Found that if I started up right aways as soon as I put in the key...it started fine. Thought all was good again, so I began running to car harder, and the jerking returned (rarely). Finally replace the TPS with a small 'S' shape screwdriver and notice no change. Not sure what else to change...MAS, spark plugs, belts, hoses?