Van shaking at stop lights

The shaking is typical of a misfire, most commonly due to worn spark plugs or lack of scheduled tune-ups. White smoke is a sign of burning engine coolant due to a leaking cylinder head gasket. The clue is the level will be dropping in the coolant reservoir. That leakage can also cause a misfire if it is bad enough.

Not if it is burning coolant as the smoke suggests. Have the cooling system pressure tested. If it does not hold pressure it could be bad head gasket(s) or a crack in a head or block.