If it worked right for a couple rides, possibly the cable stretched a bit or the clamp might not be holding quite as tight as you need it to.

You probably know all this, but in the remote chance you don't...

Step 1: Undo the cable clamp on the FD
Step 2: position the STI controls so the cable is as long as possible
Step 2.5 Return the adjuster so it is down as far as possible.
Step 3: pull cable through the clamp for the FD as far as it will go (may use pliers)
Step 4: Tighten the cable clamp on the FD

If this doesn't fix it, you may need to experiment a bit with FD position (height on seat tube and rotation to seat tube axis)

If still not working, your FD might not have sufficient travel.