Heyo,

Iruka is a very crucial ninja overall in the exams, he'll be very useful in general. Also, it's not that easy to replace him and I would suggest you that once the treasure of the sage hits up, to invest towards Iruka 800-900 coupons to acquire him.

For 140 exam, did you try to use Lightning main, Guy, Kimimaro and a barrier ninja such as Darui for example?