When sitting at idle, my engine hesitates and when I press the gas pedal, it hesitates worse. I can also hear sounds coming from the engine like I have a vacuum leak somewhere. In addition, the brakes on the rear passenger's side fell down on to the rotor when trying to change a flat tire and the Engine light on the dash is on.
Hello. It sounds like you have a series of issues going on with your vehicle. The engine hesitation and lack of power are more than likely also going to reflect the Check Engine Light. If you are getting a hissing or vacuum noise then I would typically start by checking all of the hoses under the hood while the engine is running and identify if any of the hoses are loose or bad. If they are fine, then the PCV system should be checked for leakage. Depending on what is found I would also scan the computer for codes to see what the computer is seeing. Depending on the codes there may be other issues going on.
If the brake pads actually fell out of place then they may have been put in incorrectly, or they will fall out if the brake pads are worn down and if the rotor is undersized. The brakes will need to be fully inspected to identify why they fell out.
Finally, there can be many possible reasons for the engine to hesitate while accelerating. Some of the possible causes include problems with the fuel pump, throttle position sensor or dirty fuel injectors. I would have a certified mechanic diagnose why your engine is hesitating.