is there anywhere that is common to get a vacuum leak on a 95 millenia? i posted a previous post about my car idling fine but then bogging down and backfiring when any hard throttle is applied, i can hear a vacuum leak and it increases as i accelerate, i just can't find where it's coming from. also i'm not getting the voltage i'm supposed to be getting on two or three oxygen sensors, anyone have two or three go bad at once?