U need to look under the hood, go to injection pump. There is a lever for accelerating, if u push back ward it should stop the engine. Forward increase throttle.
Sounds like one of your main vac line had worked itself loose. Lucky that u still have power brake, as PB runs off the vac too.
Just trace every vac lines, see any loose or dangling, worse scenario u need to bring it to a MB shop , should only take 10 mins for someone who knows, and 20 hrs for someone who doesn't know.