jdm209boi

ok i learn as i go on fixing car.. so i need sum help.. ok i got a 2000 civic st coupe with a b18a1 motor.. when i start the car my rpm is at about 25.. then when it is warm up it drop to about 16 or so.. here another problem when i b smashing in it.. run great untill it in netural it idel bad goin about 2000 to 3000 rpm goin up and down.. man it freaks me out sometimes... so if anyone can help me i will thx u very much of da help..