I had this problem with my passenger door some time ago, it was a small spring in the latch mechanism that had rusted and broken. I found a guy on ebay from across the pond who sells the springs. hardest part of the whole thing was the getting the teeny tiny new spring in.

 

I removed the interior window channel rubber scraper thing.

got in there with a tight hook made out of coat hanger.

Pulled in the latch release mechanism, opened the door.

adjusted all the pull rods, there are nuts on them and you can tighten or loosen the nuts, effectively shortening the throw on the door pulls, lubed the hell out of everything, and she's right as rain now.