Read the owners manual. find the idle adjustment screw and screw that a little. Wd40 all parts. The speed control cable may aso be causing it to never fully get back to the idle position.
A vacuume leak at the intake manifold or vacumme hose can cause a high idle. On carbuerated vehicles the idle adjustment screw may be set to high. On fuel injected vehicles, the Idle Air Control(IAC)...
adjust and tinker with the fuel delivery to the carbs.Check the bracket holding the cable to the carbs. Mine was idling high, I just pushed it back to a reasonable idol and it's been fine ever sense....