CEDAR FALLS, Iowa — David Johnson scored on a 1-yard run with 1:59 to play to give Northern Iowa a 21-17 victory over Youngstown State on Saturday.  Johnson carried the ball eight times on the winning drive, and caught a 32-yard pass from Jared Lanpher.   A pass-interference penalty also helped Northern Iowa.  Lanpher connected twice with Terrell Sinkfield for touchdowns for the Panthers (7-2, 6-1), who kept their hopes alive for a Missouri Valley title.  Kurt Hess threw a 38-yard touchdown pass to Will Shaw early in the fourth quarter to put the Penguins (5-4, 3-3) ahead 17-14. Jamaine Cook ran for 90 yards and a touchdown for Youngstown State.