Put a stock BOV on (if you have access to one) or a plumback BOV and then reset the stock ECU
90% of the time this is the problem. It has nothing to do with the valve sealing, its got to do with the way it can operate when you come off throttle. It can let some of the metered air out, the ECU will throw to much fuel in (Because some of the metered air is gone) and this can stall the car or get it close to
Even if you dont think its the issue, try it anyway.
By the sounds of what you are doing, the AAC valve solenoid will be opening fully and might just be enough to keep the car running. From what I understand, the AAC valve never gets to full open under normal conditions.