Help P300

Ok so here’s the deal. My kid bought a 2005 A4 1.8quattro automatic.
It was sitting in this guys garage for a long time. Initially was getting the 0171 and 0300 and all the missfiring codes.
Since then I’ve done the following:
New O2 sensor (upstream)
New MAS
New plugs and injectors
New gasket (found oil on a plug)
New battery
Flushed the coolant
Oil change and flush
New air filter

Everytime I fix something and clear the codes it runs a little bit longer with no issues.

Oh and I ordered that Vanne
06A129101F (cleaned the old one but it had so much crud in it I don’t know if it’s working right)



So I’m hoping that fixes the issue.

When I start the car it runs good for 2-3 min then it start to misfire and make bad sounds like it’s going to back fire.

Like I said I’m hoping it’s that.
Besides that I’m thinking fuel filter?
Vacuum leak?

Just not sure what to do next. At this point I’m committed. And it’s absolutely beautiful. Oh and once on the highway it runs like a dream. So just not sure.
Any help advice guidance would be greatly appreciated.