Maybe the distributor? A ground?

 

How about the speed sensors(s) on the transmission? Can't recall if these have 1 or 2 sensors, but when they go out the car can act "confused", stutter, stumble, shift weirdly, etc. Those can trigger a CEL, but not sure if they always do when they have issues.

 

here are my suggestions in any order you like...


fuel filter...(you said there were maintenance issues)
distributor (cap and rotor button...points? vaccuum advance hose)
Ignition leads...(maybe...but a cheap fix)
ignition coil (maybe.....)
transmission flush (do this anyway...since it affects your wallet in the long run)