the ecu wont give a water type error more of random sporadic errors ie abs, idle etc the only way to check fr water is to take it out and look inside, the car is out of warranty so opening it wont really matter as long as you do it indoors and try to prevent static.
shouldnt think so, removing the ecu has the same effect as removing the battery.
might be wrong here but isnt the immobiliser part of the ecu circuitry?
what makes you think its the ecu getting wet that causes these problems?
have you checked other things like the throttle body?
does it only do this from a cold engine?