My son's 97 Escort recently developed an issue running and idling very rough. I am not big on car repairs but can do some basics and have fair troubleshooting abilities. The car starts right up when cold and idles fairly well for 15-30 seconds then the idle speed goes down and gets rough. I took out all the plugs (which look fairly old and the gaps varied widely) lightly sanded them and regapped correctly. The #1 plug wire is different than the other 3 but all look fairly new. When I checked the sockets on the coil pack, #2,3,4 were all clean and shiny but #1 had a big "crater" in the side and was filled with black dust/powder. I thought aha! and tried starting the car with it disconnected to verify not firing - the car would NOT start. I also saw a spark from the wall of the socket go to the body of the coil housing. I blew out the dust and cleaned the interior with rubbing alcohol and applied a little vaseline to the connector on the plug wire (like 2,3,4 had). I then tried starting with the #3 plug cap disconnected (it was quite wet compared to the other plugs) and the car DID start up but with a loud tapping (which went right away when I reconnected the cap?). After all this the car DOES accelerate and run much more smoothly, but still has the rough idle.

I'm not a total idiot and know I need to change those plugs, plug wires and ignition coil very soon (and will soon as preventative maintenance) but money is very tight and I don't suspect the plugs or wires as only the idling issue persists. I searched the threads here for ideas and Autozone for testing advice and right now I am going to try <1> cleaning the throttle body and idle air control motor, <2> try gently tapping the IACM and see if the speed changes, indicating it's defective <3> ohm out the ignition coil and <4> check for a vacuum leak even though I don't hear any hissing and have no idea where to look.

Any other advice or guidance would be GREATLY appreciated!

every thing your doing you are doing right and i suspect a vaccum leak on the idling. and that coil sparking is not good so that maybe your problem also. i could tell you how to check for vaccum leak but others don't agree with the way i've been doing it since i've worked on cars. i'll tell you what i use but i'll end up getting into argument. i use carb cleaner with straw on it and just spray a little on vaccum hoses and when i use carb cleaner and when i find vaccum leak it will idle up. now i never said that ok? i've heard of them using starting fluid witch i have never done and they use water in spray to check your wires. but anyway your on the right path..good luck..

I agree it sounds like a possible vacuum problem.
YOu can use any fluid really... my preference is soapy water, or sometimes I just use my Simple Green sprayer if I have plenty to spare. When the fluid covers the area where the leak is then you should hear the engine settle down and idle normally for a moment until the fluid no longer covers the leak.
My suggestion would be to look over the vacuum hoses at the top of the intake manifold and look for cracks and dryrot. Usually, if the leak isn't there, then it is in the intake manifold.
Do more troubleshooting and see if you can locate a leak.