My buick issues
Hey everyone, new here and having some issues with my sisters buick. Let me start from the beginning. Burning coolant and missfire. Intake gaskets were a obvious so i started there. Removed manifold and found gaskets had already been replaced and didnt look to be bad. Found lots of coolant in oil. Proceeded to do headgaskets. Now i have everything finished. Car starts but runs horrible. Barely idles with missfire. I ohmed plugs and coil packs. All good. I moved to the mass airflow. Unplugged it and car runs so much better with a constant idle and no missfire, cool, so i replaced mass air flow... Not cool, stills runs terribly with sensor in but decent with it unplugged. I have been going over the basics. Making sure i didnt leave something obvious but this is stumping me. Now let me say i am a mechanic but for diesel engines and trucks. I have plenty of gasoline and car knowledge just not as much experience hands on with cars. Im confident its not a mechanical issue as the car runs decently with mass airflow unplugged. Just not sure where to go from here. Any help is appreciated.