Stalls when Cold or wet on 1998 Oldsmobile Aurora

Censer issue? Whenever I go through a car wash the car stalls. Whenever it rains really heavy the car stalls. I recently drove 400 miles in a snow storm and now the car continues to stall no matter if its dry or wet. The previous owners (grandparents) have had the car tested to be told. There is nothing wrong.
Any ideas as to why it likes to stall when wet? I found if I shift into neutral and keep the rear defroster on. The RPMS stay at 1... and the car does not stall... However, That is not the solution.

Asked by for the 1998 Oldsmobile Aurora
try cleaning the throttle plate, the thing that opens/closes when you step on the gas. if it is very sooty it can cause a low idle too low to keep engine on. thats my guess if you are saying it wont stall when engine rpm is kept up. use a can of carb cleaner and an old tooth brush or rag.
The Check Engine light never seems to go on. However, whatever is creating this issue is def. exposed to the elements and sits under the car. Would they actually place the computer within site of the road?
I will be taking the car to a GM Dealer/Garage rather then a standard Mechanic. Hopefully since the car is regularly shutting off they should be able to find it. I can't be the only one suffering from this issue. Anymore ideas would be gratefully excepted. I don't want to be bluffed/yanked around by the dealer.
In Mid Jan I had the car serviced at a local GM Goodwrench. They replaced the ISC System (Idle speed control) and crank sensor. They tested the car and called to tell me It was working. About 4 blocks from the dealer the car stalled on me... I returned the car thursday it is now Tuesday. When I called they told me they are now looking into the fuel pump.
I did a Google on the problem and found that replacing the Idle control valve worked. Is the ICV and the ISC the same thing?
1 more answer
Need to have the vehicle's Engine Performance System Inspected, clearly the first shop did not know how to find the problem. it sounds like the computer is getting wet. it is usually under the right hand of the dash under the glove box area. Do you ever have a Check Engine Light on?