1999 Mercury Villager

Car recently died. Replaced battery and it started again but when I accelerated, the car only putted along and died again. Had it towed to mechanic who told me it was the distributor and the alternator. $1000.00 later both were replaced and I thought I was all set. Until I started driving it again and the van would shake uncontrollably at all stop signs and lights. Took it back to the mechanic and was told that one of the cylinder injectors was gone. $200.00 later again I thought I was all sign. Started the car no shakes, no loud noises took off okay, but now when I'm at a stop sign or light and put on the breaks, the van still wants to accelerate. The engine has a "reving" sound and when I go to accelerate, there's a loud bang and the van goes.
The ride is pretty smooth, its just when I need to break. Can you help me figure out what this could be?