Any major exhaust leaks, a major exhaust leak specially if your o2 sensors are located in your cat and the leak is between your header and cat can cause stalling. I know because I did a temp ghetto rig install on my cat to the header and had a decent leak. The leak resulted in stalling when coming to stop lights and not taking it out of gear soon enough, stalling when turning and taking my foot off the gas momentarily, and at times after warm up a crappy idle. Now when the car was still cold and the ecu holds the idle a little bit higher i didn't run into this, it was once the car was warm it would start stalling. My fix was to hook it up right getting rid of the leak, now idles perfect and doesn't stall. Just an idea.