When I start my car, the engine revs up to 5,000 RPMs. In addition, the RPMs seem to stay up high when stopped at a light.
Sounds like you might have a large vacuum leak. Think of your engine as a big vacuum cleaner. If the vacuum cleaner has a restriction then it slows down, if the port is completely open it goes as fast as it can. This is what happens with your engine. An un-metered vacuum leak will cause a symptom similar to what you are describing. There are other things that can cause an issue like this, but vacuum leaks are common. A mechanic, such as one from YourMechanic, can help you diagnose the cause of your engine running high and make the repairs that are needed.