Is It Time For a Tune-up Yet ? Dieseling, Exhaust Odor, Rough Running

Dieseling

This also is known as "after-run." The engine keeps chugging and coughing for several seconds or more after the ignition is shut off. Causes can range from inferior gas to excessive idle speed.

Carbon in the combustion chamber also may cause dieseling. 

Exhaust Odor 

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. 

Does it occur when idling? When accelerating? At all speeds? Your best bet is to have a qualified technician perform diagnostic and tune-up services as needed.