I faced same problem. Culprit was Turbo was not spooling up. I am not able to recall how those guys corrected it. But they didn't charged any money. I got my car back in half hour. I was lucky as I faced this problem within 1 km for service center. & if you experience black smoke, low mileage than hose connected to turbo is culprit. It develops crack where clip is tightened. I faced both problem in life of my linea. In such condition engine works normally means turbo and all. But because of leakage in hose pipe. you will feel little heavy vehicle/less mileage/dark back smoke.