fast idle in drive,park

"Sometimes" the engine will begain fast idle 1700rpm for no reason when warm.
Sometimes will will drop back to normal. The only cure so far is to replug the TPS or restart the engine. Then a while later it will happen again, maybe days,weeks. No ses light. Doesn't seem to do it in very cold ambient temps.
I've replaced TPS, MAP, cleaned idle valve. Everything else seems fine.
I'm about to install a n.c. pushbutton switch just to disconnect the TPS for a moment as a last resort. Garage is no help. I fear a bad computer.
Any suggestions?

sounds like a bad ECT, quite common, replace with the "new style" brass tipped ECT from saturn - http://www.saturnfans.com/forums/showthread.php?t=24003

thanks , looks like that did the trick. If you told me 10 yrs ago my temp sensor had anything to do with idle I'd have to hit you in the head with a wrench.
I am glad I didnt bother to drain the coolant, it was just a trickle when I removed the sensor, not the flood I was expecting. I couldnt have drained it anyway, not familier with Saturns weird petcock which seems to need a special tool and which leads me to yet another post.