2000 Saturn SW2 Engine RPM not stable

When I start the engine (Outside tempurature 72 degree) the RPM immediatly goes to about 2000 and comes down to just below 1000 in about 15 seconds. Put the car in drive rpm picks up without touching accelerator and I have to keep puttiing car in neutral when coming to stop signs and red lights in order to stop without having high rpm's damage transmission and brakes. When driving about 40 to 50 mph and let off on the accelerator the rpms do not come down and when I put the car in neutral the RPM's stay at 22 to 25 hundred and when I stop at a red light the RPM's slowley come down to idle about 950 RPM's. After the car is heated up the rpm's stay at 950 until you put the car in drive. No check engine light comes on at all. Could you help me? Lead me to a solution? Could it air entering below the throttle plates. Engine is the fuel injected dual cam. Thankyou. Bob