I just bought a 2011 Malibu with 190k miles and vie got all its issues ironed bout except this random rough idle, that only happens after driving for around half an hour or so. When you come to a stop it will stumble and misfire bad sometimes stalling out, sometimes if you put it in park it will return to normal idle, other times it will continue to misfire until you either give it a rev or restart the car. only code present is p0300. Worth noting that I replaced MAF as well as the coolant temp sensor for other issues it had, however the stalling was present before we touched it. We had a code for i want to say it was intake air temp, which was part of the MAF so I replaced that and that code went away. Stalling unfortunately persists. also the p0300 is always "pending code" but i haven't gotten it to go to active and illuminate the light yet. I've been told the coil packs and plugs were replaced when the issue started, and they gave up on it. Any advice would be appreciated. I haven't had a expensive scanner on it yet so my information is limited for now.