2001 Daewoo Nubira very rough idling on a cold start

Rough idling after sitting 4 hrs can smell gas occasionally inside car when this happens. Rpms rev high then drop down acceleration drops but quickly returns to normal. This is now even happens on warm starts. Timing belt has been replaced injectors cleaned the only thing not replaced is pcv valve because I cant locate one.I really want to fix this car because I am not happy with anything new to replace it. Thanks lk