High idle
 

I've got a 2003 Sable, that idles high, especially when it's cold. After it warms up, it's still high enough to propel it too fast on some roads. When I stop, sometimes it idles normally, but more often than not, it idles high, and after I come to s stop, sometimes it dies, and others, it idles down. None of the places I've taken it to can figure it out, other than to throw money on trying different parts changes. Any ideas?