the most common running problem on the obdII cars is the cyclonic valve on the bottom of the intake has blown, it's the horible modern bmw design of a pcv valve that every bimmer after 96 comes with, it has a diaphram in it that splits and makes a huge vacuum leak, the easy test is spray around it with carb cleaner and see if the idle is effected, i find it hard to beleave it's not kicking up any codes as the obdII cars are overly sensitive to stuff that doesn't even make it run bad
all america wants is cold beer warm cat and a place to take a poop with a door on it