Before reading this....When it comes to explaining things....i could be the worst so bear with me plz.

I just got this BMW *manual* about 3 days ago. It has a "brand new" motor with "1*,*** miles on it"....it looks like to be true (not so smart about mechanics but he is my friend so i doubt he could be lying to me)ANYWAYS when the car is idle it is revving itself up by idk 1100-1300rpms and it continuously goes back and forth revving.
He says (not word for word but something like it) the car has been sitting in the front yard for about 4-5months and since it has a new computer and engine you have to "abuse" it or basically wear it in.
*one other thing is the throttle in the engine (were you can rev up the car while you are outside the car) the cables are loose, like it is missing a piece.*he said he tried it but thats not the problem*

so if you guys know any idea what could be the problem or my friend is right...THANK YOU VERY MUCH for reading this long boring paragraph lol...but lmk plz.