First of all, it is highly unlikely this can be fixed without the help of a MB shop. There are several causes for this, and without a diagnostic scan you are wasting time trying to figure it out. Virtually any fault with the electronic accelerator will do what you describe. We need fault codes. You need to take it in, and get a diagnostic done on it. Could be anything from a bad sensor to CAN failure. Might just need the throttle stop relearned and dtc's cleared.