Can somebody tell me why my car engine running very high?

My car is Renault scenic RT 1999 1.6L. Everytime I have problems when I ignite the engine because it will go dead if I am not to run it for a minute in 1500 rpm. However the engine is going to run around 1250 to 1500 when it is running for 3 miles away. In this case, it cause me difficulty to engage to the reverse gear with noise in the clucth. Could somebody why the engine running so fast.