Your Subaru Justy keeps stalling and sputtering in the silencer while on engine brake?

The reason why the truck moved is bescuae it has more torque. That is basically the amount of power an engine produces without the accelerator being pressed. The cars engine was unable to produce the amount of torque to move it's entire weight. There is all kinds of science behind it, and my science I am telling you probably isn't completely accurate, but knowing it will not be extremely helpful. I had the same problem you did. To overcome it, what I did was (if your on level ground) take my foot of the brake and apply to the gas so the RPM of the engine rose a hundred or two. Then you gradually take the clutch out until it is moving. If you are on an incline, it is even more difficult. You need to push the gas more, even for the truck if it is really steep. Good luck!