It will hiss when the accelerator is idling or lightly stepping on it. What happened?

Depending on the location of the sound source. Possible reasons are:

1

Generator belt slipping;

2

Two nuts of the front drive shaft are loose;

three

Exhaust of pressure relief valve;

four

The valve clearance has changed, the locking is not firm, the valve stem and transmission part are worn, and the valve clearance needs to be readjusted.

Hope to adopt ~ blessing!