Q: Car is making a hissing noise during acceleration.

Hi There, There are many things that could be caused by this, however a a common symptom of a vacuum leak is a hissing that will become more noticeable during acceleration as you describe. High idle speeds or in some cases rough idle and stalling are also signs of a vacuum leak. When a vacuum leak is present in an engine, this causes an excessive imbalance in the air/fuel ratio which creates a loss of power and causes the motor to run at a much higher RPM as a result of the increased oxygen present in the fuel charge being injected into the motor. I would recommend having an expert from YourMechanic come to your location to diagnose your vacuum leak as these can be very difficult and time consuming to trace.