91 voyager 3.0

91 voyager with 3.0 motor, i replaced the timing belt o2 sensor and cat converter in order to pass emmisions, now have new problem. if vehicle sits longer than half hour when we start it we have to let it idle for about four minutes before it runs right. seems like idle goes up and down to the point when it almost dies then it raises to to high before it settles at right idle. i left ac compressor off becouse it did not work anyway. set timing to specs. no check engine light. passed emmisions. any ideas or help would be appreciated.