Intermittent miss ansaturn 2000 sl 2

Saturn 2000 sl 2. Hard miss whenever starting from stop sign or when put under load. Did complete tune up, with all new parts, changed valve cover, new temp sensor, car shows no codes, misses when driving at normal speed maybe once or twice in 5 to 10 miles. But at every stopping of the car, when you acceleerate to move one or two HARD misses. Has killed on two accasions at stop signs when trying to start but re staarts fine. A past saturn mechanic now a gm dealer mechanic said that once in a great while the older saturns would show this condition. He thought they used to reflash the computer for a possible fix. We have not flashed the computer yet. He said it had to do with the computer not reading the sensor from the knock sensor correctly. Have also replaced the throttle position sensor. Thanks for any advise.