Nothing.
I love the car. An extremely smooth ride and a pleasure to drive.
I drive about 500 miles a week and have never had any problems with the car at all.
My family and I took a trip to South Carolina last summer and the kids were comfortable and had plenty of room to sleep and stretch.
I love the car so much that I have parked it for the last year so I could save it for trips and special occasions.
I just hope that letting it sit won't damage anything internally.
Although, I try to start it and let it run for a few minutes every week or so.
My gas mileage was a lot better than the pick up I drove back and forth to work.
If the digital miles per gallon is correct, I averaged about 30 to 32 miles per gallon on the highway.
If I didn't have a kid in college and another one graduating soon, I'd trade this one in for a newer model.
My Dad had a 92 De Ville, and traded up to a 98 De Ville Elegance.
He loves and cherishes it.
As a matter of fact, he and my mom are leaving for Florida tomorrow and he can't wait to get it on the open road.
I don`t recommend that you let the car sit, because it leaves your tires in serious danger of dry rotting, and later blowing out on the highway. I just had that happen to my 93 Deville, and not only did I have to have all four tires replaced, I also am having to have a section of exterior trim paneling replaced that was torn off by my blown tire. Other than that, you should be fine! I just don`t want you digging a $500 dollar hole in your pocket the way I did!