merging onto the freeway bout an hour ago in 4th gear at around 50 i changed lanes and gave it a little gas and the engine started to make a knocking noise and was riding jerky so i let off the gas and had to find an exit. i drove the car home at slow speeds and no warning lights came on about the engines sudden rough idling until i was a mile from home, the light is the yellow engine one and at idle the engine is knocking and shaking any suggestions? its done the knocking underload before but this time it messed up and the dealership said they couldn't find anything (mini center) this time they will