Your Toyota's Positive Crank Ventilation (PCV) system is designed to allow the engine to breath fumes from the oil compartments. The fumes are then burned through the combustion process.
Over time engine oil becomes contaminated. Contaminated oils are high in Hydrocarbons (HC) and will contribute to a rich mixture.
We'd recommend getting your Toyota 4Runner's engine oil changed before the smog check.
posted by SmogTips Support