My van runs rough at startup, and it vibrates when idling and driving slow. It runs better when at an average speed but occasionally pops. It also idles low. I have to put it in neutral at stoplights or it will almost shut off. Also, the throttle body wires (I think that's what they are called) are loose, and the radiator leaks.
The rough running is most likely due to an engine misfire. Depending on the mileage of your van, you may need to have a tune up done which may solve the misfire problem. It is also possible that your ignition coil may be faulty which can cause of the misfire condition as well. The ignition coil is a common failure in your particular vehicle. I recommend having a mechanic diagnose the vibration and rough startup of your vehicle. They will also be able to look at your throttle body wires and radiator and let you know what needs to be done with those concerns.