Need a picture.

Does this have a plastic intake manifold? If an engine backfires through the intake it could cause the issue you describe.

On non MB specific engines I've seen exhaust valve rockers come off and cause severe intake backfires. There is also the possibility of a ignition problem that fired the spark plug as the intake valve was open causing an intake backfire as well.

With such a intake manifold vacuum leak, the engine can run away since air is being admitted through the broken manifold and not through the throttle body.