stalls when put into park

I'm posting here for my mother, as it's her car that's doing this.

Sometimes when she goes into park, the car just stalls, and no trouble code is produced. A scanner shows everything is fine.. When the car is driven, it works fine, no other problems, just stalling when going into park..

What could cause this? I'm personally baffled, but I'm thinking it's an idle speed thing..

I believe her car is a 2000 model.. It's for sure is a 4 cylinder though (as her gas milage rocks much better than mine, lol.......not to mention, she told me)

possable tps problem.

I'm no expert, but I'm thinking it wouldn't be idle speed related or throttle position sensor, simply because it would theoretically also stall when put in neutral. The tps and idle speed would be the same there as in park. It's worth checking out though.

The rpm will go up when shifting into park. also a leak in a vac line could make it stall.