One thing I'm starting to suspect is the BAC. I read somewhere that the idle should drop if you unplug the BAC (makes sense.) I went and unplugged mine while the car was doing its pulsing idle thing and nothing happened, absolutely nothing (no drop in revs, didn't skip a beat in its pulsing).
Also, while the car was running, I unplugged the boost sensor. Nothing happened when I unplugged it, but when I went to plug it back in, the idle would smooth out for 2-3 seconds as I inserted the plug, but would go right back to pulsing.
Interestingly, the dealership tested one of my junkyard ones and said was good... I wish I knew someone else around here with an S4 FC to try it out on.
I'll try to get a video of my problem tomorrow (I'm sure the neighbors wouldn't like it if I went out right now and started up the FC with no exhaust connected
)