During a smog check, if the ignition timing check does not have manufacturer's engine speed tolerance, what is the acceptable idle speed range?

In the context of a smog check, the acceptable idle speed range serves as a critical parameter for ensuring that the vehicle's emission control systems are functioning correctly. When the manufacturer's engine speed tolerance for ignition timing is not specified, it is permissible for the idle speed to vary from the specified idle speed by up to 100 RPM.

This range allows for some variation in engine performance due to factors such as environmental conditions, engine wear, and minor adjustments that may be present in the vehicle, while still maintaining compliance with emissions standards. An idle speed variance of 100 RPM is generally considered a reasonable tolerance that does not significantly affect the overall performance or emissions of the vehicle.

In contrast, narrower tolerances would increase the risk of failing to account for normal engine behavior, while a wider tolerance might allow too much deviation that could lead to higher emissions. Thus, a range of within 100 RPM provides a balanced approach to assessing idle speed during a smog check.