Somtimes when I start it idle is fine 700rpm sometimes it idles to high 1200
on highway when it is running okay the rpm is 2500 @50 mph when it is running to high the rpm is 4000 @50 mph. Anyone have an idea what's up?

 

Welcome to the forum ,if this car is fuel injected I would clean the throttlebody,with a throttle body cleaner not carb cleaner,also check for and slack return springs.Good luck.