1992 Ford Mustang intermittently runs poorly at times

Computer problem
1992 Ford Mustang 4 cyl Two Wheel Drive Manual lots miles

On cold start runs good for trip. On second start up runs good for a while, then for 5-15 seconds at some point it will run very poorly (like on 1 or 2 cylinders) then recover and run 100% fine.

suspect computer, coil, ect, problem is, it runs fine most of the time and it is unpredictable when it will happen.

any ideas on how to test or what to replace first?

Thanks,
kpg