Apart from changing the ECU or using an oscilloscope on the fuel injector, I feel like I’ve tested everything else. It was intermittent for awhile, then would get worse when it warmed up, now it idles horrible and when I unplugged the third cylinder spark plug nothing would change, but if I unplugged another cylinder then the car would stumble more and get worse. I confirmed spark but tried different wires, changed the distributor cap and rotor (from another volvo but in way better condition), swapped plugs, swapped fuel injector plugs, swapped fuel injectors from another car, did a compression test which it seemed to pass (went up to 150psi, from 60 to 90 to 120 and stopping at 150ish).

What am I missing? I was so sure that it was the fuel injector, but it apparently wasn’t. It did run smooth once for about ten seconds, when i had fuel injector connector 2 and 3 swapped then started misfiring, and at that moment I could feel the car stumble when I unplugged injector 3. Using the obd diagnostics I can hear the injector click so it’s getting a signal. I was thinking I could take a spark plug out and unplug the spark plugs and turn the engine over and see if any gas flies out of the spark plug hole? I was also thinking I should try setting up my pocket oscilloscope, but I wanted to knows if anyone has experienced something like this first.
Thank you everyone!