One part of the CARB/EPA coordinated In-Use Automobile Emissions field study of 1991 carried out in the Los Angeles area was the phase to examine the operation and emissions characteristics of high emitting carbon monoxide (CO) and hydrocarbon (HC) vehicles. In the part of the study, high CO and HC emitting in-use, consumer vehicles were detected by the cross-road remote sensors and pulled over for I/M testing. Vehicles were selected from those tested on the roadside inspection for further testing on a portable dynamometer set up in a nearby park. The selected vehicles were chosen by the author and had to meet the qualifications of having good tires, no coolant leaks and no exhaust leaks. The dynamometer test took between 20 and 30 minutes and was voluntary.