1999 VW Jetta 2.0 has codes P0304 and P1582. What should I look at first to fix it ?

This is my sons car and with the check engine ligt on we can't get the state inspection renewed. I am trying to see if it is something that we can fix. In the last year we have replace the timing belt and put in a clutch kit and replaced the radiator fans. The car drives Ok but has a lumpy idle. once you give it some gas it revs just fine. I have a code reader and have erased the codes but they come back. The P0304 is Cylinder #4 misfire and the P1582 is Idle Adaptation at Limit