CEL light when it rains

Hi gang, been a while. the 2001 Sportage now has 60k on the new engine, still chasing the P128 CEL light. changed the thermostate to 195 deg. been ok for almost 6 months. every so often it trips, when I go through a puddle. I bought a code reader and keep it in the car and just reset it. what could be cooling down that fast that it trips a code? am I missing a cover somewhere when they switched the engine. I know there is a stud missing that held the plastic engine cover on the passanger side. I have not figured out how to replace it, since the engine that went back into the 2001, was actually from a 2000, which didn't have that dumb cover. I have the cover in place with a clamp I made of strapping iron, wrapped around the intake mamifold and held down by a nut and bolt. this only happens when I run through a puddle and splash the engine. other wise except for a window motor failing, everthing has been running great (for a change).