'93 100: transmission won't down shift

[E. Roy Wendell IV]

I don't know if this particular car has one, but this symptom in 
general is usually attributed to improper disengagement of a lockup 
type torque converter. I can't imagine that having the transmission in 
any gear would cause the symptoms that you describe as the conventional 
fluid coupling part of the torque converter should be transmitting 
little to no power to the rest of the transmission at idle speed. The 
lockup type torque converter has an additional clutch mechanisim that 
locks the input and output shafts together in order to eliminate the 
normal slippage that occurs in the fluid coupling and thus improve fuel 
economy. If the locking system were to malfunction you would 
essentially have a clutchless drive train as there is no conventional 
clutch (it's an automatic) and you no longer have the disconnect 
provided by the fluid coupling because it's locked.