Yup, thats gonna be a throttle cable, my m3 did it but it was on the cruise cable, when I took my foot off the gas the cruise cable could get jammed and it would keep going. Try just disconnecting the cruise cable if you have it. Otherwise replacing a throttle cable isnt hard.
You can also try spraying wd40 down the throttle cable, I didnt have much luck with it but give it a shot.