91 escort high idle

I have a 1991 escort with a 1.9l. When driving the engine idles extremely high about 3500 to 4000. It will start fine and then it will start idling high when you start to move. It will kick down a few seconds after you come to a stop.
We have looked around for any vacuum leaks and did not see any. We have also replaced the TPS because that is the only fault code that comes up when you plug in a code reader. We have also tried replacing the Idle Air Control Valve, with no improvement.

Just wondering if you ever solved this one...

I had the exact same problem and it was the IAC. In your case I'd be testing the Collant Temperature Sensor.