Intake valve deposits are hardened carbon deposits which form on the back side of the intake valve. The degree of deposits vary depending on many factors like fuel properties, driving habits, and engine family. Intake valve deposits can cause driveability concerns as well as increased exhaust emissions.
Excessive intake valve deposits can cause an engine to run excessively lean while cruising and accelerating, and excessively rich during deceleration. During lean operating periods, NOx emissions are elevated. During rich operating periods, CO emissions are elevated. The amount of emissions increase has a linear relationship with the degree of deposits on the valves. At some point, deposits can effect emissions enough to put a vehicle out of compliance in an Enhanced I/M test.
False Intake Air Entry
Typical false air entry locations include; intake manifold gasket, intake air ducting, throttle shaft bushing, etc.
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