2000 Mustang V6 bout 156k Mech issues

[Ramsin00]

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 !!!

 

[antineutrino]

The rough-idling happened to my 02 V6 Auto when I bought it last week (previous owners changed spark plugs on the morning of the purchase), but only on a cold startup. I usually gave it a minute to warm up, and then it drove fine. Having put over a 100 miles on it since in the past week, this seems to be a non-issue now. Could be an ECU self-adjustment.

The other reason could be carbon buildup, if you have a lot of miles on it. Not sure about the hiccups at high-speeds.