Chadular

Hey Guys I bought a 95 z28 with the LT1 in it and seems run and drive awesome has around 125,000 miles on it. I typically dont have any problems but it seems like when i'm just coasting through town my service engine light will come on and my water temp will drop like 30 degrees. I can put the car in neutral shut it off for a few seconds start it back up and the light wont be on any more. When it shuts off sounds like a big fan or something like that powering down. Sometimes the light will shut off on its own but not usually. Anybody have any thoughts of what this could be for me? maybe it happens more often than i know. I really dont know. Thanks guys.