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AV-SCANNER / Service function guides / Engine and oil
This guide walks you through a complete rough idle diagnosis, from understanding how the idle control system works to performing a structured, step-by-step procedure that isolates the root cause. It is written for working mechanics and experienced DIYers who already know their way around an engine bay and want a repeatable diagnostic method rather than guesswork. You will learn how to prepare the vehicle, run the tests in the correct order, interpret the results, and verify the repair with measurable outcomes. By the end, you will be able to diagnose an unstable idle confidently across a wide range of vehicle types and know when to stop and hand off to a specialist.
Guidance is general and covers many makes. Exact procedures and values vary by model, so confirm them in the factory service information for your vehicle.
Download all 12 sections as a branded PDF to use in the workshop.
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