Smart Fortwo - vibration - plumbago

Between 2500 and 3000 revs when under load a strong vibration is trasmitted through the car. My local garage Smart Truro had the car twice, second attempt found a broken heat schield, this replacement under warranty has lessoned the sound level but not the cause.Any suggestions as the car will shorlly be returning to Smart Truro further investigation of the cause and my ongoing moan regarding fuel consumption at 34mpg I feel this to be excessive. I have been given the usual response of it will improve after 3000 miles, it has done this and no it has not improved. I have noted that other owners have been told after 6000 miles things will improve. Can anyone help?

Smart Fortwo - vibration - unthrottled

This problem needs context since it is subjective. What car did you have prior to the smart? The reason I ask is that under (admittedly rather extreme conditions) 34 mpg might be acceptable, 3 Cylinder engines are inherently unrefined compared to 4 cylinders-which is why a lot of manufacturers shun them. That said, smarts have gained a reputation for poor build quality and ho-hum fuel economy. There really isn't anything smart about them at all!

Smart Fortwo - vibration - Collos25
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Smart Fortwo - vibration - Collos25
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Smart Fortwo - vibration - Collos25

Something wrong with my computer.

The Smart is renown here in Germany for its extremely poor petrol consumption there are far better cars available with more room that are more economical do not have odd size tyres and are far cheaper,in the reliability stakes the Smart is a none starter they came pretty near the bottom of the ADAC league of unreliable cars if everything is not set up perfectly they vibrate like hell a nieghbours bought one for his wife she wanted it as an accessory to her handbag I think has had a vibration under power for two years it comes and goes I thing its to do with the tyre pressures or the engine mountings,having been in it once I would much prefer to walk or catch the tram.

By the way they have nothing to do with DB they are made in a contract factory somewhere on the French / German border I believe.