I had the same problem in my old Mondeo. After 3 weeks in the garage, the mechanic said it was the turbo, but I got a neighbour to look at it. It was a circlip missing on the throttle cable. That was it. 5 cent worth of a circlip after 3 weeks in a garage! Have a look in the engine bay and check to see if the throttle cable is sticking. That doesn't explain the knocking sound though, so I'm no help on that front. Steve