I purchased a preowned dealer loaner Mercedes Benz E 350 4 matic with full warranty & clean car fax. I bought the car for its reliability & safety. I have had the car for two months & have had three incidents of intermittent lack of brakes & sudden unintended acceleration just barely avoiding accidents. I took the car for service & they were not able to find or duplicate the problem. I no longer feel safe in this car & told them I did not want the car back. They are currently driving the car to try to duplicate the problem but may not be able to recreate the problem. I would like to settle the problem amicably but they are giving me a low-ball appraisal of $10,000 less. I would like them to locate another car. I do not want to get taken on trading & getting a similar vehicle.

Pre-owned dealer vehicles are usually given a careful once-over before they are re-sold, and indeed, Mercedes-Benz vehicles do have a very good reliability and safety record. It seems unlikely that they would have re-sold the vehicle with any mechanical faults. I hate to tell you this, but most cases of lack of braking combined with sudden unintended acceleration are usually the result of driver error, or some obstruction (such as a floor mat or other debris) interfering with braking.

I worked for Motor Trend for more than ten years, and our best technical driver, Mac DeMere used to give this suggestion when drivers complained about both a lack of braking and unintended acceleration: "If your car is accelerating instead of braking, lift up your foot, and press down on the OTHER brake pedal."

Mac had extensive experience as an instructor for several racing schools and was a driving coach for numerous racers and test engineers. He competed in NASCAR’s Southwest Tour and IMSA’s Rolex 24 at Daytona. He co-drove to five wins in 24 hour races and scored several other victories on road racing circuits, oval tracks, and autocross courses. I trust his automotive advice.

I would suggest that you ensure your floormat is not obstructing the gas pedal. (I'm sure your dealership would have ruled this out.) And then take a few moments to familiarize yourself with the locations of the brake and gas pedals to ensure you're not accidentally stepping on the wrong one.