Not that I think it's practical to go line by line through a combo list rather than drop it down and use scrollbar to advance row by row or page by page, but you could use keydown (I think down arrow is key 40) and advance the combo list index value, as in
Me.myCombo.ListIndex = Me.myCombo.ListIndex + 1
Of course, more code would be needed to back up in the list, as well as trap for being at the beginning or end of a list. Big pain for small gain.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.