I posted this in the garage section, didn't get much response. I am new here so I am a little unfamiliar with the site, but getting use to it. So I am posting my jeep situation here. I started with the cooling system a while back, now it seems a mechanical problem now. So a while back, I cleaned out the cooling system. Flushed radiator and heater core. Heater works great now. I have heat. Cleaned out the carb air inlet, choke, not sure what it is called. It was gummed up a bit. I do have a straight six with fuel injection. Ran good for a while, now I noticed a rough idle, it goes up and down, slightly not real bad slightly noticeable enough, on park and when I get up around 40 miles an hour the jeep starts knocking back and forth, I then put it in neutral and it smooths out after a while. Not sure if it is the engine causing the knocking (jerking, changed to jerking, because it is a jerking motion back and forth not a knocking sound.) or the trans or something else, like the universal joints. Usually universal joint problems don't cause a jerking motion or not in my experience with other types of vehicles. I think it may be beyond universal joints. Universal joint problems usually cause your vehicle to move when parked on an incline unless the joint is so bad it is loose. I do know it needs new plugs, they haven't been changed in a while, so I may need to do that, may help with knocking, but that in itself wouldn't cause the jerking back and forth as I am driving. Any tips helpful. Thanks a bunch!