I have a 2006 Mercedes CLK500 and when I'm driving it sometimes my rpm goes up and down. Additonally, when I stop at a light and try and take off, my car goes slowly or not at all, but the rpm goes up very high and it sounds like I need to change the gear or something, however, it's an automatic. Then, it will not idle down (switch gears) on it's own once it starts doing this, I have to literally turn the car off, then back on and then it will run good for a few days, then do the same thing again! What could be the problem because I don't have any lights on saying to check anything. Please advise because it's nerve wrecking being at a light and not knowing if your car is going to take off correctly or not!