If you have a class with unused imports as well as missing imports, the first time you run "organize imports" (ctrl shift o) it will only add missing imports. You need to run it a second time to remove any unused imports. For example:

import java.util.ArrayList
import java.util.Random

class Test {
  val a = new ArrayList[String]
  val b = new EmptyStackException
}

java.util.ArrayList is imported and used, java.util.Random is imported but not used, and java.util.EmptyStackException is not imported but is needed. The first time you run ctrl shift o it will add in an import for EmptyStackException, but it will not remove java.util.Random. If you run it again, then it will remove java.util.Random

I assume this is because the class does not compile until EmptyStackException is imported, so I'm not sure how feasible this is to do.