Why is my car "revving up" like this?- Toyota Avalon 1998

Please help me! My car is revving up when it's in park for seemingly no reason at all. I don't have the slightest idea as to what the problem may be. In addition to this, if I try to put it in reverse or drive, it sometimes shuts off and I will have to go through a lot of trouble to get it started! Please, I know it's a car-guru out there that can help me!!!

Test your engine coolant temperature sensor. It could cause symptoms like this.

I once had a Honda Accord on which the alternator failed, but it didn't go bad all at once, it just caused the car to do strange things. It would run just fine, then out of nowhere the idle would go up between 2500-3000 RPM and the battery light would come on. Then one day the engine just stalled while I was still moving and would not start again until I got a new alternator and battery. It's something to look out for.