What if Jetta's speed rises when shifting gears?

The question you asked may be because the carbon deposit blocked the idle passage, causing the throttle valve or idle motor to be stuck or out of its adjustment range, or because too much carbon deposit caused the throttle valve to be stuck and unable to return, causing the idle speed to rise after receiving oil. You just bought this car. It is estimated that the main problem is that the throttle has too much carbon deposit.

Mind you, there are many times when the idle speed of oil collection will increase after clearing the throttle. This is because when cleaning the carbon deposit, the carbon deposit solution enters the throttle shaft, which causes the throttle shaft and the valve body seat to get stuck. It is also possible that the throttle valve cannot completely return to the initial position set by the manufacturer because it is not initialized after cleaning, and the throttle valve has a large opening, which leads to the phenomenon of high idle speed.

I suggest you go to a 4s shop or repair shop for a comprehensive inspection to clean up the carbon deposits.