I have a 2002 SL1 Saturn that I bought in 2001. For the most part it has been a terrific car, with a few major problems. However, over the past 3 years, I have been having problems with the RPMs. It has grown increasingly bad over the past year. When I start the car up, the engine revs up and the rpms jump up to 1500 or even 2000. Not until i put the car in reverse does it come down a bit. When i come to a stop at a stop light or stop sign, it revs up again. When i do put in park, the rpms jump up again to 2000 or 3000, and when i shut it off the car shakes. I have taken it to many shops, but no one can figure out what’s wrong. The last time i had it in to my regular car shop they fixed the EGR Valve and thermostat. The guy said that it could solve the rpm problem, but it hasn’t. My friends have suggested spark plug problems, but the shop has already checked that out and said it wasn’t part of the problem. The engine light and oil light have not come on. What could be the problem? I’m really tired of this being a perpetual problem. People have also said that the rpms are supposed to rev up a bit while the car is in park, but this isn’t normal. after driving the car for almost 10 years, I know it’s not normal. It the only problem right now, but it needs to get fixed. Thanks for any input. I appreciate it 
You need to have the engine checked for a vacuum leak. This is a common problem that will cause unstable engine speed. Deteriorated vacuum hoses are a very real possibility on a car of this age. Intake manifold gaskets are also a common problem with this engine. You can check for vacuum leaks with a can of carburetor cleaner, sprayed on parts of the induction system. A leak is found when a change in engine speed is observed.
The high idle might be caused from a defective Idle Air Control valve. Locate IAC valve on the throttle body, and while the high idle is occuring, tap on the IAC valve with the handle of a screwdriver. If the idle speed changes replace the IAC valve.
Tester