The second-ranked McIlroy, from Northern Ireland, had four bogeys and two birdies in wet and overcast conditions at Carton House on the outskirts of Dublin. McIlroy hit only five of 14 fairways and took 34 putts.
"At the moment, no aspects of my game are strong and I'm just feeling a bit lost at the moment," he said. "It feels good on the range and I can hit all the shots, but when I get out on the course it really does not seem to be there.
"Off the tee, I am missing one right and then missing one left and it's just not going where I want it. It gets you in two minds every time you are playing a tee shot. The game is just not coming easy to me at the moment and while I was struggling at this point last year, I was able to turn the corner in the middle of the summer and have a great end to my season. I don't know whether it's a matter of trying to play my way out of it or just keep grinding away on the range or whatever."
Floren, from Sweden, had a 6-under 66. He drove the green on the par-4 13th and holed a 20-foot eagle putt.
"I just came out and hit everything really, really pure," Floren said.
Uihlein, the Madeira Islands Open winner last month, is making his 10th European Tour start of the year. The former Oklahoma State star won the 2010 U.S. Amateur.
Lowry, the 2009 winner at County Louth as an amateur, had six birdies and a bogey played alongside McIlroy.
"I was just chomping at the bit to get out there this morning and I was just trying to play me way into the tournament nicely so I'm really pleased with a 67," he said.
Hoey said wife Barbara had their first child induced last week so he could compete in the event.
"It's great being a father and already it's added a new perspective to my life," said Hoey, a four-time European Tour winner.