1999 Ford Escort Escort occasionally running on 3 cylinders

First thing you should be doing is going to autozone and having the codes read, its free. I have a 97 escort and had the same problem. The codes I got were cylinder misfire 2 + 3. Start at the spark plugs and work your way backward, usually you wont find a problem with the wires unless they have been resting on the metal which can cause a short, the coil pack is what was my problem both times, I have replaced 2 coil packs, (about $50.- A piece, )
the wires were fine and changed the spark plugs just for the fact that they got all gunk out because of no spark. The coil pack is so easy to do, four screws, and a connector plug, it sits on top of your engine. I hope you have a book for your car, if not ask at autozone for a diagram. Thats where I would start. If it is left to run on less than your 4 cylinders (3 or 2) for too long it could cause some serious damage, so good luck. These cars are great once you get to know what they need. Hope it works out for you. Let us know how it goes.

I now have a new coil, new plug wires, new plugs, and a new gas filter and it hasn't fixed the problem. In fact, I think it's worse. My mechanic pulled the connections on each of the injectors yesterday and they all appear to be working - what else could it be?

Well the verdict is in - upon start-up yesterday the engine sounded like a lawnmower on a rock. Mechanic thinks probably the piston is gone.