You got a pod?
You're sucking air into the engine, it's either going on the MAF causing it to stutter or it's actually leaning out the cylinders, one of the two, I wouldn't worry about it, just try and find where it's sucking the water from and maybe revise how it's made.
When I cleaned my engine bay once I had a little stutter because some water was being sucked up by the pod and my car would jerk around a little at those mentioned revs, it went away not long after though..
But I tell you in heavy rain I had to pull over!