There shouldn't be much to the airbox itself. The MAF and IAT sensors could have been momentarily sprayed with water, causing a drop in the temperature of the intake "air" as read by the computer. Or a drop in the velocity and pressure of incoming air, which is more likely.

Last summer I had occassion to remove and take apart the air box on my Impala. The 2006> Impala air box is designed with an air intake that is trumpet shaped and takes fresh air through the front shroud from just behind the left headlight. This intake extends across the interior of the box (I'll bet shawnvw has a nice graphic). If water splashed up under the front driver side (behind the headlight housing), water or mist could easily enter the box. However, the paper filter stands vertically between the inner end of this intake and wouldn't allow any moisture to get to the MAF sensor. There are a couple of electronic "thinges" at the bottom of the box that were quite warm to the touch. I guessing these ^ provide heat on cold mornings and normalize air temps. I'd check the air filter to see if there was any damage to the element which might restrict the air flow like it would if momentairly wet. My senility waxes and wanes these days.

haha. Is senility a word?

I guess it is now. :D

I'm thinking it's more a state of mind....then I forget.

Hi, I have the exact same issues with my '07 Impala. Everywhere I bring it to can't duplicate it, or find anything wrong. But we know it's happening and it's very annoying! Only self remedy I tried was new ABS/speed sensor cables which didn't help. Did you ever get to the bottom of it? Thanks!