My mustang is having quite a few problems latley when in park it sounds like it is accelerating and releasing gas the rpms go upto the 1 and it goes even higher if i spin the wheel back and forth but when i turn it all the way to the left it stops and goes down , i know i have a bad O2 sensor i may have had it like that since i bought the car i know that cant be good but just something i felt like i needed to include ive had the car for about 6months almost 7 months and recently ive also had ripped off the transmission mount and have replaced it with a new one and it stopped vibrating so much but now it kicks back when getting to a high speed on the interstate it feels as if the car is being held back i need advice pleasseee !!!