2000 Mercury Sable - Stalls in Park when heater is turned off?

Question

I have a 2000 Mercury Sable, 120k miles.

The engine starts and runs fine at all speeds until I park the car and turn the heater fan dial to the off position. Then the RPM's bounce from 1k down to 0k over and over until I shut off the engine or switch the gear back to drive. The dashboard lights also dim while the car is stuttering and the car acts like it will die.
>This is repeatable.< >no check engine light comes on< I have not yet let the engine die completely but I'm sure it would if I didn't either turn off the engine or shift to drive. I can also save the engine from stuttering in park by applying the gas. Any ideas would be greatly appreciated. Again, has only happened while the gear is in PARK and I turn the heater fan to the Off Position. Thanks so much.

Answer 1

Check out the ground wire between the engine and the frame. If that's bad the electrical stuff will all go crazy.