I have a Dart with a slant six that doesn't get driven much. I do try to start it every so often but it seems it is getting increasingly difficult to keep running and the exhaust smells terrible. When I go to start it, if I don't let it warm up for a good 10 minutes, it will stall when I put it in gear. Then I can't get it started again. I have to let it sit for a day or so and try again. If I let it warm up, it doesn't stall out when I put it in gear and it will continue to run seemingly O.K. but the exhaust reeks. I would appreciate any suggestions on what may be wrong.