Ignition diagnostic monitor (IDM) ???

I know this is not the "right" forum, but a lot of good fixers meet here .... so I'm posting my Ranger question(s):

I'm working on my SIL's '95 Ranger 2.3 ... and without a wiring diagram.

It's begun to run poorly at times ... the engine skips and shakes. I can disconnect either of the two ignition coils ... no effect. I can disturb all the harnesses in the engine compartment ... no effect.

There is a engine light. Codes 218, 222, and 224.

218 and 222 have to do with a "ignition diagnostic monitor (IDM)" ... WHAT IS THIS "IDM"??? Is it part of the PCM (or ECU, or MCU or whatever the controller is called on this model?)? And where is the controller located on this truck?

224 is "PCM detected coil 1, 2, 3 or 4 primary circuit failure". ???? Any clues on this one?

Any help would be appreciated.

BTW, the (230 k miles) truck is fairly well maintained. Plugs, cables, IAC, DPFE, EGR, EGR regulator, Fuel pump/sender, filters, etc ... have all been replaced in the past 12 mos. Until this mysterious episode began, it was running very well.