It wasn't on an Xterra, it was on a Jeep. But it uses the same flat style air filter which coupled with the foam cover was what caused the problem. A cone filter is unlikely to saturate on the top unless fully submerged. A flat filter only has one dimension with which to breath and it is pointed straight at the inlet hole in the l/f fender well. It will saturate very quickly due to that design. The foam does a great job of holding water. You will notice Ian that I said it takes less water to saturate them. It may only hold a cup or two of water, but that is all it takes to restrict air flow to the motor and hence makes my point. Switching to a cone type filter will help reduce that possibility by making the filter area 3 dimensional. You have more surface area for the water to saturate, hence more likelihood you will have a clear area for air to flow. The best fix is to stay away from water. But here in Florida, that is next to impossible. I stand by my assertion.