95 Intrepid -Plumes of Gassy Steam!

[ChrisandLois]

Help! Our 95 Chrysler Intrepid purrs like a Kitten when it is parked and you can let it idle - literally for hours BUT if you try to drive it - 5 minutes out and Plumes and Clouds of steam pour out and envelop everything - it looks like it is on fire! Park it and turn it off and it purrs again!
A series of events seem to have caused this. There was a little oil on the Valve gaskets so we had those changed ( If it works - don't fix it!) Within 60 miles the Check Engine light came on and it was missing badly - New Spark Plug - Purring again. So--- while it is idling away at home I - in my wisdom - decide to try the AC - Turn it to cold and press the button - PLUMES of STEAM! Dripping from the converter and smells of gas but isn't.
Anyone care to hazard a guess. The 2 mechanics that have looked at it have decided the engine is toast even though they have let it idle for over 2 hours and it never even heats up. Does not burn or leak oil either.
HELP!!