Okay, there is something wrong with your idle air bypass solenoid. That would be the codes 81, 82, and 12.
The 21 is your ECT is out of test range. Did you warm up the car before doing the test?
The 94 and 44 are thermactor codes. Do you still have an air pump?
The 4 is half the number of cylinders your engine has.
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351W 89 Mustang GT Convertible