OBD-I jumper codes not working

Stepson recently just bought the car listed above (GT) for his first car. It wasn’t running. Checked the fuel system and it seemed good. Looked into the ignition system. Found that the pip signal to the ignition control module wasn’t working (removed wiring harness to ignition control module. Used a test light and on crank it should have been flashing. It didn’t.) I also used a meter on the coil and found the resistance read low. I replaced the distributor, ignition control module, coil, and plugs. Car started but ran really rough. Tried to pull signals using the OBD-I port under the hood. The service engine light just stayed on solid. I also tried using a test light on the port and it just stayed solid as well. I removed the battery cables and pulled the wiring harness to the PCM. Connected battery cables back and turned the key on engine off and the service light was off (so nothing should be grounded). Car is running rich (new plugs already have dry soot in the same day of changing them. Black smoke also coming out of the exhaust when giving it gas), OBD-I port isn’t working to get codes, and the ignition control module still isn’t getting the pip signal (test light flashing on crank) even after changing all the ignition components. Is this all related possibly? Possible bad PCM? Thank you in advance for any help!

To add, I found if I remove the big vacuum line that runs to the three nippled “valve” or connection right behind the throttle body. (Not sure what you call it) The car idles much better. You can give it throttle without shutting off. This valve has a vacuum line that connects to the EGR and two other things. I replaced the EGR, and this still happens. Not sure if this issue is related to the first topic. Thanks again!