Cadillac Repair: Deville quits when climate control is off, loud thump, radiator fan

Question
My car is a 1994 sedan deville with the 4.9. It has 62,000 miles and recently started acting up at complete stops. If the  car has been driving 15 minutes or more, it will quit at every complete stop unless the climate control is on. When the climate control is on (any temperature, any setting) the engine will maintain normal rpm at every stop and everything seems fine. But if the climate control is off when the car stops, a loud thump can be heard about two seconds after stopping, then the engine quits. The engine starts up just fine every time, there are no warnings or messages on the display. I did notice that a radiator fan stopped working. The front fan works, but the rear fan does not work. I plan on getting the fan checked out, but if the vehicle was overheating wouldn't the display warn me? I am puzzled, the car drives like it's brand new when the climate control is on. I bought the car a year and a half ago, it has undergone no major repairs. The car has never been crashed and I am very easy on the accelerator. The coolant was flushed and the oil was changed shortly after I bought the car. The oil has always been changed on schedule. The transmission fluid was exchanged only a few months ago. What is going on, what should I do?

Answer
Most likely a residue buildup within the throttle body and or the EGR ports need to be cleaned out as this IS very common. The reason the car runs with the AC on is that the idle speed is increased by the AC compressor operation. There is a possibility of an IDLE SPEED CONTROL MOTOR fault and or misadjustment.