I have had several issues in the past with Hondas more than anything a hard to find idle has sometimes lead to a cooling/heating issue. I have found that a clogged ports in the throttle body where coolant passes and other coolant lines and hoses can cause this rough idle. I had an issue in the past where I had a very tiny coolant leak that was hardly noticeable and I got an idling issue, my needle eventually crept it's way up from a normal point, corrected it and idle went back to normal.
As far as a vacuum leak goes, like BIGBOY said, starting fluid only when it's cold. I don't like using it personally. Brake parts cleaner works too, with the propane you could get one of those BernzOmatic tanks that you can find at your local hardware store with the valve on it opened wide and run through all your vaccum hoses, manifold etc. Or depending on your budget, you could get your car smoked, either at a shop or if you know someone with a smoke machine. (they are EXTREMELY EXPENSIVE)
hope this helps!