1997 Plymouth Voyager smoke from the exhaust tail

1997 Plymouth Voyager Four Wheel Drive Automatic
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in the begining there is white smoke coming from the exhaust pipe...and it stop after a while....and especially when iam on the reverse mode.....and after moving the smoke stop....but when i stop and press on the accelerator pad smoke come again(does the spark plugs do this as i think it should be replaced as the car is lightly shacking)