Causes can range from inferior gas to excessive idle speed.
Carbon in the combustion chamber also may cause dieseling. The smell of rotten eggs comes from the catalytic converter part of your car's emissions control system. The odor can be due to an engine problem or it can be a sign your car's catalytic converter is malfunctioning. Rough Running A malfunction in either the fuel or ignition system can cause an engine to run rough. It also can be due to an internal engine condition, such as a bad valve or piston.