Missfire from idle to aprox 3000rpm

try adjusting ur alternator. Tighten the little bolt on it. I had the exact same problem. I had to get a new alt, because it damaged the old one bad. Ever since, havent had a problem, and she purs fine through all tach levels..

Any codes?

The inability to get codes doesn't sound good. Being an '89 the computer should be a basic swap for most years 88-93. Unless the previous owner did some hanky panky stuff with the wiring and computer......???
Based on the parts you have already swapped or checked, there is one more you might consider. The TFI module there on the front of your distributor. My car developed a similar type miss, and only at certain rpms AND a certain throttle setting!!! I finally took it to the Ford dealership and they found an "intermittent" TFI module. They told me it was not uncommon for these modules to develop a "soft" spot where a certain rpm range might get blocked out and cause problems. Indeed, a new module did fix the problem.
Just another item you might consider.
Good luck,
Ken