A beetle's cold car began to shake and sometimes stalled.

Because the diagnosis result is carbon deposition, the direct cause is insufficient cylinder pressure. You can check the cylinder pressure with the cylinder pressure gauge first. If the cylinder pressure is really insufficient, it is generally serious carbon deposition. A more direct way to solve this problem is to remove the cylinder head and clean up the carbon deposit inside. However, if your situation is not very serious, you can buy the original G 17 gasoline additive, fill it up as required, then run a long distance of one or two hundred kilometers at a speed not lower than 100, then add enough gasoline additive to the next three cases of gasoline, and then add it according to the instructions. At the same time, consider whether you have changed your previous refueling place.