Try simple, cheap remedies first.

The mirco-switch that tells the idle control valve that the throttle position is "in the idle position" that is no gas pedal pressure could be out of adjustment. You need to hear (or feel) a definite click when the throttle position returns to rest. If not, loosen its mounting screws and position it until it does click.

Another simple, cheap, possible fix is a loose connection at the idle switch or idle control valve. See if there are any frayed or abraded wires anywhere.

Another possibility is that the idle control valve is sticking. Take it out and clean the inside with carburetor spray.