sounds like an IAC issue (Idle air control). This allows air to pass when the throttle butterfly is closed to maintain idling conditions. It sits atop the TB. Check your throttle cables to make sure they are moving freely and not getting caught when returning to idle position, if they are fine, you can remove and clean the IAC with TB cleaner, but that's probably just a short term fix, probably need a new one.
At least clean and see if the problem goes away, then you'll know that's the prob.