What should Jetta engine do if its neutral speed increases?

Regarding the increase in the speed of oil collection you asked, the reasons may be that the idle speed control device is stuck or out of its adjustment range due to carbon deposits blocking the idle passage, or the throttle valve is stuck and cannot return due to excessive carbon deposits, which leads to the increase in idle speed after oil collection. In many cases, after cleaning the throttle, the idle speed of oil collection will increase. This is because when cleaning the carbon deposit, the carbon deposit solution enters the throttle shaft, causing the blockage between the throttle shaft and the valve body base. Sometimes the throttle valve body needs to be replaced seriously. I hope my answer is helpful to you.

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