Gasoline motor vehicle organic emissions are elevated by reduced ambient temperature operating conditions, and the practice of warming vehicles with extended idle periods, as is common during winter months. Total hydrocarbon, carbon monoxide, nitrogen oxides, and formaldehyde emissions are examined under idle operation at 20 F, 40 F, and 68 F with six gasoline fueled vehicles (including noncatalyst, early catalyst, and late model catalyst) and a methanol fueled prototype vehicle. The emissions were substantially reduced by the late model catalyst control technologies at all temperatures examined. Formaldehyde emissions were elevated with methanol fuel. (Copyright (c) Pergamon Journals Ltd. 1987.)