Anyone's 453 run a bit rough at idle? I bought the car brand new and it wasn't this rough for the first 5k miles. I have tried different gas, etc asll the same. I took it to Mercedes of Sacramento and they said 2 things. 1 they have never even had a newer smart in there and 2 it was normal. If I rev it to like 1200 RPM's it is fine and smooth but just sitting at a light its definitely rumbling.