What's wrong with the black pipe under the Cruze air filter with soot black?

That's engine carbon deposit. Failure to clean the throttle for a long time will lead to this phenomenon. Please ask the master to wash it off with carburetor when maintaining it. The accelerator should be cleaned regularly, otherwise the carbon deposit in the engine will accumulate more and more, and it will be expensive to wash it again. There is something wrong with the car, find the car master. 4S shop professional technician, 10 minutes to solve.