Visiting Iran shouldn't hurt the immigrant visa. However, it's possible that it may trigger additional security checks, resulting in an extended AP after the interview. Nobody can say for certain what happens with the security checks, so this is just speculation. Officially, there is no reason that a visit would impact your case.
Although it should not matter, you cannot predict what will happen in the next months or years while you are waiting for the green card. Iran is one of the countries in the ban and people who have visited any of the countries on the list are scrutinized more for entry, even if you are not from the country itself. Even though the ban was deemed unconstitutional, I'm sure they will try new ways to ban people from entering or sending them home or making it harder for them to get visas. So it could affect you being allowed to visit you parents on a visitor visa in the US. Or it could delay your green card process because they need to do more background checks for you. Decide at your own risk.
