Your throttle cable could be frayed where it goes through the firewall,
that will hold the throttle open a little and give you a high idle, check the
cable at the carb, it should not be tight and holding the throttle open, see
if you can force the bell crank (the thing the cable pulls on) closed and if
that lowers your idle, if not, adjust your idle screw to about 900 RPM warm
Wild