I have a 2000 RX 300 which has been doing very fine until yesterday. I was coasting at about 110km pH when suddenly, the car lost power. It revs on id le but will not accelerate when on the go. I have had the fuel pump changed but to no avail. There is this constant hissing sound coming from the engi ne area as if there is an air leak. Any one know what the problem could be? Thanks in anticipation.