87 T is acting up. It's missing and surging-running terrible

Unfortunately there is no obd data link connector on these old z cars. Your only option if you want to use onboard diagnostics is the manual procedures.

http://xenonzcar.com/z31/ECUcodes.html

Did you also replace the ignition transistor as well? Other wise, check fuel pressure and vacuum. Report back what you find.

Did you also change spark plugs?

after checkin vac lines, checking electrical connectors/grounds for corrosion, and checking codes.

I'd go with what Richter said. i had a really random intermittent issue and the PRW-2 sorted it out, they're a plenty in junkyards.

http://www.xenonzcar.com/z31/prw2.html

This is what i use to diagnose most VG's I come across and it usually has been one of these problems.
"A few things you can try.

Unplug O2 sensor completely, it is not necessary in normal driving around town and the car should run good without it. A bad o2 sensor can cause it to run somewhat differently than it should, however.

Check ignition timing. This is what it might be… The vg30 will run with the distributor a tooth off, but it will feel slowwww. verify this with a light.

The injector plugs are finicky. Unplug each one and you can use a very small flathead screwdriver to gently bend the prongs inward to make sure they get a good contact. [this is what i think your issue is]

If that doesn't fix it. Then you should disconnect the battery, unscrew the ECU plugclean it with contact cleaner, then carefully put it back together making sure that it goes on straight and tighten snugly. then press on the plug all around firmly with you thumbs to make sure they are all contacting well.

Regarding the boost gauge. You should get an aftermarket boost gauge right away, you won't blow a gasket at idle but if it is doing something like the wastegate not opening, then you could cause some damage."

These are sure symptoms of a bad AFM. If you can, borrow one from a friend and test it. You will be glad you did. Bad 02 sensor, incorrect timing or bad injectors will not make it surge. Injectors rarely go wrong. If it is an injector not firing, that cylinder will miss a beat. It will make it lose power instead. It will not surge.. DO NOT mess with the ECU just yet UNLESS you know what you are doing.

Mass Airflow or cracked intake boot most likely

Yes nickvance, a leaking inlet track after the AFM will also contribute to RPM fluctuations.