Engine revs by itself

First, when I start her up, I always let the engine warm up for a few minutes. When driving and getting over 40mph, the engine revs and drops, revs and drops. My foot is steady on the gas pedal. The revs are maybe 100rpm, nothing to make the car accelerate. After a few minutes of this, she levels out and runs steady. Anybody experience anything like this? Also, she runs really hot if I get stuck in traffic. I rigged up a way to vacuum the radiator and cleaned out the stuff that got sucked into the shroud. If I am moving, the temp is fine. Thanks!

Which transmission does your car have?

Hunting RPM sounds like it could be vacuum related, maybe a small leak someplace. Its also possible the throttle position sensor is dirty causing some low rpm fluctuation. Overheating...how hot is it running? The colling fan switch doesnt turn on until coolant temp of around 230. Chris

Stock automatic

Almost decks the needle so I have to pull over and stop. Thanks

When you say "almost decks the needle", I assume you mean the engine revs up to almost the red line?  If so, it sounds like the symptoms you originally described have changed and/or getting worse.  Correct?  What happens after you "have to pull over and stop"?  How many miles are on the car?