I have a 04 quadcab,4.7L with 88,000. I have a intermittent vacuum leak. Loss of power, poor mpg, brakes not a firm(pedal),ect. decided to listen for vacuum leaks and long and be behold the purge solenoid is hissing, but not all the time. I read the function and operation of it. Nothing says it hisses while purging. Is this my problem?