Why does the idle speed fluctuate after cleaning the throttle body?
2 Answers
This is caused by excessive carbon buildup. Here are the relevant explanations: 1. Cause of carbon buildup: During the intake process, impurities accumulate over time on the throttle plate. As time passes, more and more carbon deposits form. When the throttle plate moves back and forth, it encounters resistance. Over time, the engine's computer adjusts the position of the throttle plate. This means it treats the carbon buildup as part of the original structure, effectively preventing the throttle from fully closing—it only closes to the position of the carbon deposits. 2. Reason for high idle speed: After cleaning the intake throttle, the plate still moves according to its original travel, meaning it doesn't close completely. However, since the carbon deposits have been cleaned away, the intake air volume becomes slightly higher than normal, leading to a higher idle speed.
I recently experienced unstable idle after cleaning the throttle body too, which is quite common. The main reason is that the throttle position might not have been fully reset during cleaning, causing the engine ECU to fail to relearn the new position. If small dust particles remain after throttle cleaning or the reset isn't done properly, the airflow control gets disrupted, making the idle speed fluctuate. You should let the car adapt by driving it for a few days – a highway run helps the ECU record normal values. If the problem persists, check for loose throttle position sensor connectors, as a worn seal can cause air leaks. By the way, don't skimp on car maintenance; go to reliable repair shops to avoid human errors. Regularly inspect the intake pipe to prevent dirt buildup, and address minor issues before they escalate.
