Do you draw an icon card for a previously discovered room if you end your turn there? Or are icon cards only taken when the room is discovered? I could not find it clarified in the rule book
You only draw when you first discover a room
From Page 5 of the Second Edition rules (emphasis mine):
A room may have a card symbol on it. The first time you discover a room with a card symbol, you must end your move in that room and draw the appropriate card.
There is no rule instructing you to draw cards during subsequent visits, therefore you do not draw it on subsequent turns.
Given that you cannot move after drawing a card, not following this rule would mean that adventurers would only ever be able to move through one room per turn (except for those without a card symbol). That would be a slow, plodding game that would mess with lots of haunts.