Overnight joint-leader Benjamin Hebert is in outright third as he staged an impressive recovery from a double-bogey six at the ninth, the Frenchman making birdies at 10, 13 and 14 before parring in to card a 69 which kept him just a single stroke behind Rahm and Im.
"My short game in general is not good as I am making silly mistakes, so it is not good, " said McIlroy, who claimed a stunning victory last year at the K Club after struggling in previous years. "The energy generated by the crowd means a lot, I just have to try and make some birdies on the front nine".
It was the second time in three years the defending Irish Open victor had missed the halfway cut and the fourth occasion in the past five years McIlroy will sit out the weekend rounds in the premier Irish event.
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However, a bogey on the par four 16th followed before he ended the round with par on the final two holes.
"It's disappointing because I felt like I was playing well coming into the week and I need to do some practice over the weekend and get ready for next week", McIlroy said. Hebert and Im both shot 67 in their second rounds.
And the 28-year-old four-time major victor could not recover, his score of 73 taking him to a combined total of one over par at the halfway stage, ensuring the competition will head into the final two days without its marquee player.
World No. 2 Hideki Matsuyama, and the third member of the McIlroy s group, was also in contention in adding a 68 to move to nine under par.