I own a Mercedes-Benz SL320 M-reg, built in 1994. Since I bought the car three years ago the cruise control has never worked. This didn't bother me and I hadn't any spare cash to repair it at the time. After the car developed an erratic idle speed I took it to a Mercedes-Benz agent for repair to both problems. After the changing several components which were available through Mercedes-Benz on sale or return I was eventually told that the engine management system was at fault and that it needed replacing, at a cost of some £1200. Sadly they were unable to get sale or return on this article. I asked them to go ahead on the basis that this would cure the fault. It did not. I am now left with a car that is faulty, the garage has not effected the repairs I asked for and I'm to be presented with a bill for a part I didn't need. Where do i stand on this?