2000 Hyundai Accent failed the emission test, high

Did you RESET the Adaptives?.. if you didn't that may be the problem. To reset adaptives, remove both battery cables and touch the cables together for 30 seconds (60 seconds is better), then reconnect the cables to the battery -- see if that cures it. You are correct, there is no EGR valve on that engine. However, there are several other sensors which could be causing your problem.. one is the MAF, the other is the MAP and still another is the IAT and the ECT (MAF - MASS AIR FLOW, MAP - MANIFOLD ABSOLUTE PRESSURE, IAT - INTAKE AIR TEMP SENSOR and finally the ECT- Engine Coolant Temp Snsr. If any of these sensors is malfunctioning,& lying to the ECM, they could cause a 'LEAN' fuel condition and that's why your NOx's are high.