1994 Ford Probe SE Starting/idle/throttle Issues?Gremlins?

First things first,

1994 Ford Probe SE
2.0L, 4 Cyl. Engine
145,000 miles
New 4 Speed Automatic Transmission (done at about 142,000 miles)
New Radiator (small coolant leak somewhere)
Recent Tune up.
New Air filter
New Fluids

Problem:

(This is a strange one)
It will start up fin cold. It'll run fine. But after it warms up, if you stop and put it in neutral the engine rpms sky rocket (as high as 5000+). Shut it off and turn it back on and the rpms will skyrocket again (in both Park and Neutral). Drive, Reverse, 1st, 2nd and OD/OFF all work fine, engine runs a little rough and idles at 750 to 1250 (varies but usually at 1000). Have adjusted the idle speed screw a few times, have gone to a pull yard and got a different throttle body but still have the same problem. If the rpms drop below 500, the car stalls out. Once in a while, it wont start at all.

Last time we test drove it to see if we had fixed the problem, when we got back, white smoke was coming out form under the hood and upon closer examination, we saw that it was coming form a hose connected to the throttle body (I am assuming that it is where the coolant goes in to the temp sensor in the throttle body).

PLEASE HELP. None of the mechanics I know have ever hear of a car doing this.