[wiswind]

I would try cleaning the IAC (Idle Air Control).
Spray some WD-40 or SeaFoam inside it to clean and lubricate the threads of the screw in there.

The IAC takes over the control of the air into the engine (and the idle speed) when your foot is not on the accelerator. The PCM senses the position of the accelerator through the Trottle Position Sensor (TPS) and controles the idle speed by opening and closing the IAC.

The IAC is located on top of the upper intake manifold.....next to the throttle body. It is held in place by 2 small bolts....and has an electrical connection. It has a little motor inside....that turns the screw.....and opens / closes the airflow into the engine. You remove it.....and look inside....and you will see threads on the screw.

It sounds like when you disconnect the TPS, the PCM then flags the TPS as being open....and ignores that value. When the TPS is connected.....the PCM is trying to control the IAC....but it is not responding.
You can also replace the IAC, if cleaning does not help.

The only other thing that I can think of....is to make sure that there is not some kind of vaccum leak....but your CEL should light up if you had that much of a leak.
Also, make sure that the throttle linkage is not hanging up somehow...and not permitting the throttle to go all the way closed when you foot is not on the accelerator.