You probably have a broken or worn out check link. Can you feel the detents when you open the door slowly? If not your check link is bad. It's about half way up on the door aroung the hinge area. To replace it you just take the bolts/nuts off at the body and then there are two 10mm nuts inside the door you have to take off. Just take off your door panel and you can snake your arm in there with the window up.
Phil