The early 500's did have Trottle body actuator problems, which hopefully you don't have. it will cause odd iconsistent rough idling or misfiring. When you install a new one it has to "program" to your car. According MBZ this is done simply by turning on th ekey and lettting sit for a few minutes. I went through that process when I had bought a PAD chip. After putting back to stock and replacing caps, rotor etc., & then the actuator (they are expensive) when I put the chip back in my 500 ran like stink. Make sure the rotors are in good shape. They are also know for hairline arcing as they wear.
I do have one PAD 500E spare chip if anyone is interested, with directions. $100. Don't ask, it's new left over from getting for a number of 500e associates that helped me out.
Mo Eckley