Yeah, the crank sensor isn't the most fun...
There's a thing that the spark does that uses the spark advance at idle to smooth out the speed so the spark advance will go all over like that unless you pull out the SPOUT connector, it's a little grey jumper that goes into a 2 pin connector (it's behind the power steering pump I believe), that puts it in timing mode and locks the timing so it doesn't do that.
Unfortunately the diagnostics isn't great on these unless you do the flash codes (there's a thing in the tech section on an "analog volt meter" to flash codes, you can do it with just the jumper and jump in the seat and watch the check engine light, you only need a test light or analog meter for the early ones without that). In this case it would be really nice to hook into an OBD II port and watch the output of the MAF and fuel trim values but I don't know how to do that since these aren't OBD II...
That said the whole operating system on these is fairly simple, the crank sensor gives the DIS module an rpm with TDC marked, that sends a signal to the computer to fire the injectors which uses the engine speed along with the MAF output to meter fuel until it warms up then takes input from the O2 sensor to modify that. The spark advance outside of idle speed (like mentioned above) is modified based on a load table (from the MAF) with an rpm axis on the table. The fueling is using a "batch" method where the computer has two outputs combining cylinders 1 and 4 and the other pair is 2 and 3 so they both inject at the same time (similar to the ignition, same pairs, the intake and exhaust coils fire at the same time as well outside of cranking where only the exhaust side fires).
With all that there is room for there to be issues, metered air systems (those that use a MAF sensor) do NOT like vacuum leaks, my '97 got mad and didn't run right with just the hose to the fuel pressure regulator off but that was also screwing with the fuel pressure which changes fuel flow per millisecond of injection pulse...
As for what causes misfires, it's usually spark but with the redundant system these have that's less likely if everything has been checked out, there's also fuel which could be inconsistent fuel pressure from a bad pump or regulator or an inconsistent fuel injector or just a bad wire somewhere to the computer or a sensor... I would hold off on the parts cannon and maybe start with checking the fuel pressure or while it's idling grab engine related wires and start wiggling stuff.
On the erratic tach, if the engine speed isn't jumping with the tach then it could be something with the DIS module, however it works the tach signal is driven by the output to the intake side coil...
if you have any other thoughts or thing I should try please help I’m almost about to just carb and disturber swap it I hate computers
