My 01 Cadi Deville DTS has been unable to remain running. It will start, but I must keep my foot on the gas, to keep it running, soon as I remove my foot off the gas, it will cut off. During all of this,the Battery voltage will decline. Also the Service Charging System will appear. I took it a repair shop for this problem, and replaced the map sensor, and it seems to have made the problem worst.I get codes P0506 and P0507. The car idles high and idles low and the car will stall. Do you think I will still be the alternator? Any help would be very appreciated_thank you kindly!