Car accelerates on it's own?

when start the van engine idles high for a few seconds, then comes down(but not all the way)...Makes a noticable noise and the front end shakes....When put into drive all I have to do is touch the gas and the van accelerates upto 24-28 mph and sometimes higer...When go to stop, brakes grind and/or squeals(kinda like a bike when u are going fast and put on the brakes....I would like to know how to stop the van from accelerating...It's a 1994 chevy astro ext..Appreciate any advice