Why would the engine idle higher and not kick down on a 1989 Ford Thunderbird auto transmission?

A possibility is that the idle air throttle control is probably sticking. It is on top of the throttle body. I recommend replacement, this should fix your problem. Your question raises more questions: What do you mean by 'kick down'? Are you talking about the Transmission not kicking down? If so.. probable problem is the Throttle Position Sensor on the opposite side of the throttle bellcrank. Otherwise, if you are meaning the rpm wont kick down to normal, then there is a good chance you have a vacuum leak or, as said above, the ISC is gummed up or defective. To check for vacuum leak, disconnect ALL vacuum accesory tubing at the manifold EXCEPT for the Fuel pressure regulator. Plug those manifold ports and try it. Other possibilities are binding throttle cable/ trans cable at the throttle. DO NOT adjUst that throttle stop screw!!!!