2000 Dodge Stratus Car accelerates by itself

This only happened to me about 2-3 times this week at random points, but I start the car and the idling goes from 1200 to around 1600 and fluctuates, all without me touching the gas pedal. This continues in drive and reverse too-- the car will accelerate by itself even if I have my foot on the brake (in which case I have to really press hard to make the car stay in place, and I hear the engine straining because it is trying to accelerate while i'm braking). Why is it doing this? I tried shutting off the engine and restarting and it went away. That seems to solve it temporarily. Any information is very highly appreciated.