To prevent stalling in the mean- time, a faster correction to engine torque can be made by changing spark advance. While very large changes can be made to engine torque by changing throttling, actual changes take a relatively long time to fill the manifold and allow the engine to react. Throttling can come from either the throttle blade itself or the IAC motor. The largest controlling factor to idle speed is engine throttling. You can copy and paste this link to share: Ī couple layers of control are required for this delicate balance at the lowest acceptable speed without stalling. SHARE THIS ARTICLE: Please feel free to share this article on Facebook, in Forums, or with any Clubs you participate in. For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE This Tech Tip is From the Full Book, ENGINE MANAGEMENT: ADVANCED TUNING. Remembering that idle speed is the result of the delicate balance between engine torque and engine drag from loads, small changes in engine torque can yield relatively large changes in idle speed.
Following trends found under stable operating conditions at medium engine speeds and loads downward gives a better estimate of what the engine wants at idle speed. The longer pause before the next feedback signal makes it easy to over- or under-correct at idle speeds.
Because of the slow engine speed, there is a relatively long time between possible corrections the PCM can make at each TDC event. Now that the engine has been mapped under most stable operating conditions, it is possible to move on to a less stable condition: idle.
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