2001 Cadillac Eldorado ETC High Idle

My Cadillac Eldorado Northstar is having a high idle problem. It started about 2 weeks ago. I was driving and noticed that the vehicle was not decelerating normally. I had to use additional brake pressure to stop the car. When I placed the transmission in neutral, the RPM jumped up to 1500 RPM. I stepped on the acelerator and it stayed at 2200 RPM briefly and then went back down to 1500. I pulled over, turned the engine off and let it set for a few minutes. I started it back up and it idled normally.

Today I started the vehicle up in the morning in my garage. It was in "Park" and it went to 1500 RPM immediatly (like normal) and stayed there (not normal). When I stepped briefly on the accelerator it stayed briefly at 2000-2200 RPM and then came back down to 1500-1600 RPM. It will not go to its normal idle speed of 700 RPM. Please advise.

1. 2001 Cadillac Eldorado ETC
2. 30,000 mi.
3. Automatic transmission
4. 2 wheel drive
5. Strange sounds - None
6. Fluid leaks - None
7. No past repair history other than normal periodic mainytenance.