There is a little screw on the throttle body, right above where your intake system hooks up to the manifold. Adjust it a little bit. From what the Honda dealership says, Civics should be set at 600-700rpms when idle. This is with the A/C on, ofcourse. Adjust the screw just a lil bit at a time, with the car on. That should work, or it could be a problem with the Idle Control Valve.