90 Pontiac Sunbird rev's high in drive

I was given this car, but it idles high when I shift into drive but returns to normal when in park or neutral, feel as if i had cruise control at higher speeds?

 Raymond  the first thing to do is to take the car to a shop and at least have the computer scan diagnostic done to see if it's thrown a code, which will be stored in the computer itself.  Then at least you would have a starting point.  It's possible that it might be the  Idle Air Controls (IAC)  it's function is to " Adjust air flow in the idle circuit to maintain idle speed under various load conditions is fuel injected engines."  Keep in mind that these new cars are controlled by the computer.  E-mail me back on the codes and let me know what you find.Dads Shop