1990 Mercury XR4 Suddenly Idles too high

Hi there, I have a 1990 mercury XR4 thats been perfect for the last two years. However, last weekend I had the engine on muffs to check the fuel pump. Found out it was loose and tightened it back up. Started engine up after tightening the pump and suddenly it idles at 1800 rpms. I have called mutiple mechanics and they all referred to rebuilding carburators. So I cleaned them out, reset the idle mixture screws to 1 3/4 turns and it still runs around 1800 rpms. I checked the stator, trigger and switch boxes and there all good within specs of service manuel. I'm kinda at a fork in the road and dont know where to turn. Does anyone know what could cause this?