2002 firebird runs poorly and stalls after 20 minutes

I have changed fuel relays and no gas comes out of the regulator when I unhook the vacuum. The check engine light is on but I haven't scanned it yet.

Best to get code or codes scanned first that will cut out a lot of guessing but sounds like a partially clogged catalytic converter.

It has new plugs and wires. And I don't know how to clean a maf sensor. It's putting out a p0300 code. Multiple cylinder misfire.

I was thinking fuel pump. But I also seen it could be the cat. I'll disconnect it tomorrow and see if it helps.

Yeah I would go check out this link to a YouTube guy ScottyKilMer and check out what he says and help you run down the problems it could be anything from your battery to a leaking intake manifold from what he's saying so it's probably not your catalytic converter and looks like you got new plugs so you can maybe get some ideas from him hope that helps https://youtu.be/OyvdWeyDHf4

Yeah mass air flow sensor that's actually real close to the throttle body in front of it its like this little like rod thing sensor thing couple wires encased in like a I want to say like a metal rod cut out inside of it and the air blows through it that tells the computer with the airflow mixture fuel mixture should be easy you just pull off the air induction tube and it should be in there and you're only supposed to spray it with a special cleaner and you can't use just any cleaner you never wipe it or touch it you just use the cleaner to spray it and it cleans it off but that's probably not exactly what's going on but it's also good to do when you do a tune up