If you get the valves too tight you are going to burn one of them and could cause idle problems. If you are setting your intake and exhaust valves at .016 cold, you are getting them about as tight as I think you should. I am assuming that you are still using a cast iron block? I doubt that the valve adjustment as you have it set is causing an idle problem. You might want to consider for safety, setting your exhaust valves at .020 and your intakes at .018.