I bought a 2005 Chrysler 300C with 140,000 miles on it 2 weeks ago. When I am driving at any speed my car will speed up especially when I start to brake. Check engine light is on and the code is cylinder deactivation and no other history. I have been to multiple shops who can not find the problem and they say the car has to send a code while hooked up to the diagnostics which it hasn't yet. Sometimes it is harder to start taking 2 turns of the key. I had the flash for the torque updated. Clock spring replaced, oil change, new plugs and.the throttle body cleaned because it was real dirty. Mechanic thinks it is downshifting but how is that if it speeds up, it only happens when accelerating or on cruise and when I brake (weird) imagine driving with someone who floors it then takes their foot off gas, floors it again and so on, that is exactly how it feels. Has anyone had this problem or have an answer for me please! Thank you