idle/rpm gone crazy!

[wannarace928]

This is really starting to bug me, and no one can seem to figure out the problem. And its getting worse. Basically, my car starts fine in the mornings. Or usually it does. Once in a while it starts out at a higher rpm until it warms up. It drives fine on the highway, shifts fine. (at least I think so, still new to this type car) And then once you get to your destination, or get off of the highway, while the car is in drive and your foot on the brake (at a light or stop sign)it idles at around 1200-1400rmp. If you put it in park or neutral it will rev up to around 2500 or higher rpm's. I took it in for service yesterday, it has a million and 1 problems, they told me my battery was bad and that might have something to do with it, even though it is 3 months old. So i took the car to get a replacement battery today, and after they put the battery in and I started the car, it was still doing the same thing, but the check engine light came on briefly then went off while in park. The car would rev up then go back to normal then rev up then back to normal. Then I drove the car home and it has been fine the rest of the day, but I know it will do it again the next time I drive it. They checked the alternator, it is checking out fine. They checked hoses and wires to make sure everything is connected and it all seems fine. When it does this I have to press harder on the brake and it feels like it travels to the floor more than it is suppose to, and they did tell me the rotors are bad, but I am replacing all 4 rotors and pads all the way around today. But this should not at all affect the reving of the engine. Any ideas?