​​​​​​​I own a 1998 Civic ex d16y8 . Just recently the car started overheating. I checked a couple of things. Radiator works fine , fan turns on when it's supposed to , no visible coolant leaks. I put in a new thermostat yesterday thinking it was gonna fix the problem but it still overheats. The car overheats while I'm driving , needle reads about 3/4 , but it quickly comes back down in its own. Sometimes if I turn the heater on , the needle will drop back down . I just recently replaced the spark plugs , old ones looked in pretty bad shaped , one of them was somewhat white. I'm not getting any white smoke from the exhaust or any milky looking oil, so I'm hoping it's not a blown head gasket. Also I'm getting code p0505 (idle air control system) the car misfires on a cold start but then goes away after it warms up some. Any help/advice would be greatly appreciated