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.

What model and engine are we working with? If it'* a 3.1 or 3.4 head jobs can turn into nightmares. I've seen where too much was taken off the head and caused the valve adjustment be off causing a missfire.

Its a 3100 3.1

have the heads decked? change the plugs?

New plugs, wires. And checked heads for warping. The car will run without a missfire with mass air unplugged. But the second i plug it back in it stumbles and stalls.

If you have a diagnostic scanner....

disconnect the battery for a few seconds, reconnect, plug scanner in and clear codes. Even if you don't have any. This will reset all of your fuel trims back to learn mode, puts the trans back into learn mode and all other things back to "factory" settings. Restart car with MAF plugged in and see what happens.

I tried that. I think the manifold gasket isnt seated right or maybe i missed a small crack. Going to pull the manifold again this weekend and check.