Iowa can keep PSU to under 24, but it'll be tough. First, they have to prevent the big play. They might be able to survive one, but two or more is going to be almost certainly insurmountable. Even if that means Barkley keeps ripping off 8-yard chunks consistently, it at the very least keeps the clock running. The passing game isn't elite, but it's still a threat, so the Iowa defensive front 4 will need to be able to put some pressure on McSorley and force him into making bad throws (or better yet, getting sacks). The more 3rd-and-7s Iowa can force, the better.
Offensively, just run the ball well, win the TOP battle, and don't turn the ball over (I know, big surprise, right)?
Even then that might not be enough. Iowa may need a pick-six or have to do something on special teams (a KO or punt return for a TD, block a punt/FG) to win this one.