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.

 

Check for a vacuum leak.

 

aight...ill check it out.

 

yeah you should hear a faint whistling if you stick your head close by. Outside that, well shit. dunno if that even had a MAF sensor...

 

Sounds like a bad Idle stabilizer valve.

 

aight thanks

 

Yeah i'm not to familiar with those old things, but check for some sort of idle control sensors/screws/etc on the throttle body (where the cables are hooked up) or Metering devices like MAF or MAP.
Then like everybody said, check for vaccuum lines coming from the TB/intake manifold that are cracked/missing.

 

hm well, I dont know much about those old BMWs either, but I link this thread to my brother who is also registered here.

he is a Munich trained BMW Service technician LOL , maybe he knows something.

 

i've had the same problem before, check the vac lines for cracks, look for cracks after the maf in the intake, clean the maf. it's going to probaly be one of those things. also if you haven't done it in a while change the fuel filter for some reason with old bmws that clears up a lot of problems

 

aight cool lmk