An exhaust emission control system has been developed for used cars of the 1955-1967 model years. Average exhaust emissions were reduced on 194 cars by 53% HC, 33% CO, and 31% NOx. The package consists of increased idle speed, leaner idle mixture, and retarded ignition timing. A thermostatic vacuum switch provides engine cooling protection with the retarded ignition. For maximum effectiveness of the control, the engine must be in good running condition.