Ok, We bought our 620i new in 2008 and its ran fine since up till about 2 weeks ago. Its to where you start it and it will start and the rpm's will drop back to normal then it will like miss a fire or something and it will start to almost die and then when I hit the gas to go it will literally fall on its face for like 3 seconds and then it'll pick up and go but rougher than normal. Any ideas