engine accerlerates 3 diff times when slowing down

I have a 2002 Saturn SC.. about 50,000 miles on it.. when i start my car, it automatically accerlerates to about 2RPMS just by starting it up.. when i slow down, even when i push the brakes, the engine accerlerates at the speeds of 37, 20, and 10.. and when i put the car in park, it acclerates again. I know I should go to Saturn to get this fixed, but what could this mean and how much would it cost if you do know whats wrong?

will it should accelerate alittle when you go from drive to park. because you are taking the engine off a load. and also those numbers are pretty close to the shift points which withthe gears mak your engine rpms go higher but. at the start up if it maintains that then. i forget what to do when it is not so late/early ( see time post) i will look for it

yeah but when i first got this car, this stuff didnt happen.. Just the past month or two. Well at first it only accelerated at 37.. then the 20 and 10 came in, which makes me think that its just gonna get worse

You probably have a vacuum leak. Most likely, intake manifold. As far as cost, I have no idea what it costs. I fix my own cars.

sounds like it could be your idel speed sensor