Improperly Adjusted Valves May Cause Emissions Failure/Rough Idle on Toyota Corolla

Submitted by Vehicle Owner · May 29, 2025
Published by RepairPal

Problem overview

A rough idle and even an emissions inspection failure for high HC and CO can be caused by improperly adjusted valves. Also, exhaust valves may become too tight which can lead to valve failures. Our technicians tell us that regular valve adjustment inspections are a must.

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