The S-AFC is designed for Cars using a "Speed Density" calibration system which doesn't use a MAF. (typical Honda, Nissan, Toyota, etc...)
From what I have gathered from various tuners using this on a MAF equipped car like a DSM turbo, the S-AFC doesn't read the MAF signal correctly at idle causing a rough idle. Stazi (being a former DSM owner) can probably elaborate a little better then me.
-Mark
