Stat would likely ( but not always - in diag there is no always) set a P0128 ; you cleaned the T.B. , but no idle relearn, but she drove enough since for it to pick up on it. Suggesting premium was a bad idea. Car doesnt require premium, and when you start the car , first thing it does is wing the timing until it hears spark knock. GM and chrysler both had tsb's for that. Those things being said , i have no answer , but due to the nature , i wonder about cam phasers (potentially cold phaser knock before oil pressure builds) or even simple stuff like shield rattle, due to the described condition being cold start , and sounds like before actually out on the road. never had a spark knock at idle or out of gear, even on the worst sucked magum lower plenum gaskets that had let the engine coke itself up full of crankcase oil . even those cases only had preignition under load.