The problem started while driving on the highway and at the speed of 100km/h. I felt that the motor began to get slow and no response for the fuel pedal at all although I was pushing it down up to the maximum stroke, and on contrary the motor starts to sound knocking such as working with just 3 pistons, not 4. And if I pressed the pedal down the motor stays and sustain on the speed of maximum 50km/h and this is very dangerous on the highway, as you know. Please advise.

For your reference, I went to the local VW agent in my city but couldn't help me and the problem still exists (replaced spark plugs, plug's cables and map sensor) and I went there more than 3 times without any solution for my car. They work by trial and error. Thanks a lot.