1997 Mercury Villager Miss Firing

When the engine warms up it starts misfiring and gets worse and worse til it won't even Idol. If it's cold out side and the engine doesn't warm up. It runs perfect. So if I drive to work in the morning it runs as if there is nothing wrong, But as it sits there and if the temp gets up into the 50's by noon it will start fine but by the time I get 5 miles down the road it'll bearly run. I have replaced the coil - plugs - wires - cap/rotter. When I first replaced the coil that seemed to fix it for about a month, and then the same problem returned, so I got a third rotter that seemed to fix it for a day, but didn't fix anything once it heated up. Oh yeah, There is no anti freeze being burned nor oil being burned. The oil is not milky.