Okay,
My newly purchased '85 coupe with the 4 banger is running really bad.

First some history...
When I got the car (about two weeks ago) it ran as though it had a miss on one cylinder but ran reasonably well for a car that sat for 4 months without being started. Thinking that a simple tuneup would remedy the problem I replaced the cap, rotor, wires, plugs, air filter, and pcv vavle. The replaced parts looked normal. Unfortunately the tuneup did not improve it. I could tell no difference at all! So after reading some of the technical posts here I went after some of the other suspect components. I replaced the O2 sensor, air cleaner temp valve, idle air control, checked all vacuum lines, and ran a can of duralube fuel system cleaner through it.

The engine still has some form of miss - like one cylinder is not firing at all. It will idle but hunts from 900 - 1100 rpm. It starts fine and still gets about 34 mpg but it smells like it's running really rich. I have plans to replace the coolant temp sensor but I'm at a loss what to do after that.

What else should I be looking at? The EGR valve? MAP sensor? Throttle position sensor? Head gasket? Valve job? Fuel injector? Dealer diagnostics?

HELP Please!

I would first check the timing. This should actually be performed when ever a complete tune up is required. I had some bad hesitiation on my 87 duck, checked the timing and sure enough it was retarded..Adjusted it and as smooth as a babies bottom now..

How did you adjust the timing on your 87?

I'd check the compression first to make sure that the mechanicals are o/k. My guess is that one cylinder is low on compression.

yeah- compression. the first thing i'd check on anything that wasnt new.

I would also check out the Catalytic converter If it is starting to clog it will cause simular problems. Check compression to make sure you don't have a blown head gasket.
Other signs of blown head gasket is water in the oil or oil in the radiator.