JT,
I find that I have been most successful howling when I start with an interogation howl or invitation howl. Then I wait at least five minutes. I have had a few yotes come in without howling back.
When a coyote howls back at me I determine whether it is a response to an invitation or if it is a territorial howl which is shorter and more agressive. If it is only a response I don't howl any longer, I wait for a while, and if I don't see it I use a rabbit distress call to lure it in. If the coyote howls back with a territorial howl then I challenge it once to get it worked up and then I wait. If you are in the coyotes territory he will probably come check you out.
That is what has worked for me.
