low4door

hey i got a 2000 honda civic si/ex coupe automatic that is acting weird when it first starts up, the rpms go up and down like its seaching for a few seconds then goes to normal. so i thought it could be that there is air in the rad or in the block, so i tried to let out as much air as possible by letting it run for a bit with the rad cap off. did that for 30minutes. then started it up after it colded down and it still did but not as much now. does anyone have a idea what it could be or how i can fix it? thanks