my 1996 nissan 240sx (auto, 142k miles) has been having very bad shaking problems for the last 2 months. the engine shakes when i start the car, while in park, sitting at a red light, or going in reverse. Even when I start accelerating it feels like the engine is getting no power and the car continues to do this until i get around 50 mph. also you can hear a knocking sound in the engine , while it idles, or driving.all ive done so far is change the fuel filter since thats what most of my friends said to do. So any answers will be appreciated.