I have a 2013 SS with a manual trans and when on decel in neutral (clutch in or out) it will idle okay and then start surging. When it starts surging the fuel trims go to 30-ish positive just before it happens. If I force Open Loop it will idle fine. In the data log you can see the fuel trims go instantly positive and starts surging at the 5:37 to 5:40 minute area on the time stamp. I have done quite a few cars and never seen this before. Any help is appreciated and thanks in advance.