Q: Hi, my 2006 camry is having low idle rev (400 rpm), engine shakes and constant hissing noise seems to come for fuel tank. What cou

While driving suddenly the car lost power and started to stop but not died. I tried to press the gas pedal it revs but it wasn't speed up. At the same time engine check light, airbag warning light came off. I managed to drive the car back home as it happened a mile away from home. I called a mechanic and he came over and tested the battery and told me the battery is out of charge (only a month old) because the alternator is not charging the battery. I had the alternator replaced with a new one and when I started the car (the battery was recharged) it started to shake as if not enough fuel is passing with idle rev was around 400 to 450 rpm. Also engine check light came off. The light goes after driving few minutes but when idle it comes back again.There is a constant hissing noise coming (appears to be from the fuel tank). The noise was happening almost a year and no mechanic noticed it and I thought it's a normal. I need to know what could be possible issue with my 2006 Camry- Thanks

My car has 253000 miles.
My car has an automatic transmission.