while you are the first to get a P0103, another member has gotten a P2187 - system too lean at idle, while driving in the rain as well. while most people will agree that you will not waterlock your engine unless you drive through a lake, it is very possible that water or moisture can soak into or move through the filter and short the MAF sensor or cause the readings to go haywire. i suggest the next time you drive in the rain, whether you get this code or not, remove the filter after you're done driving and touch the inside of the cai pipe. if there is moisture, then maybe it's time to invest in a hydroshield.