Originally Posted by DallasGV

I'm putting my engine back together after a timing chain guide failure and noticed that the secondary air line - #11 in the pic

(RealOEM.com * BMW E53 X5 4.4i EMISSION CONTROL-AIR PUMP)

was heavily coated with carbon where it meets the block and the o-rings seemed to have shrunk as well allowing air to enter and exit the system. My car also has the low vibration at idle and it's just a theory but, I "think" cleaning the pipe and replacing the o-rings will smooth it out. My engine is not back together yet and I've replaced waaaaaaay too many other parts to know if this would make a difference in the idle by itself but I think it would. So, if someone who has the rough idle could try it - it might be a cure.