Auto or manual? Either way, you can shut it off in gear.

Some configurations used an idle stop solenoid, which is energized with the ignition on and is used to set idle speed; when ignition is off, the plunger retracts and the throttle blades close completely, stopping the engine.

Heat, fuel volatility can cause seasonal issues. If it continues, you'll want to find the cause. Any spark plug or carburetor changes or timing changes lately?