2003 l200 SATURN SURGING AT IDLE

MY 2003 SATURN SURGES FORWARD WHEN AT IDLE AND I HAVE TO USE BOTH FEET ON THE BRAKE PEDAL TO KEEP FROM HITTING THE CAR IN FRONT OF ME. LAST HAPPENED ON 7/25 AND HAS HAPPENED 4 PREVIOUS TIMES SINCE OWNING THE VEHICLE. IT HAS 15000 MILES. SATURN CAN FIND NOTHING WRONG.WHAT MIGHT BE CAUSING THIS?