I think your 99 and mine may be twins... I have been having the hesitation and stalling problems for about the last 10 months. It started off happening when I would turn the steering wheel full right or left; then backing up and putting it in gear; then cutting out and stalling when coming to a stop; and finally stalling while moving in low speed traffic to the point where it can't be driven.
My family mechanic THINKS he's isolated it to the VCT and the antipolution controls, but he's not sure yet. if you unplug the wire that sits on top of the VCT (it's the one all the way on the left on top of the VCT, sorry don't know the name for that exact plug) that seems to stop the hesitation/stalling problems, but your CEL comes on. His advice is that the next step would be to replace the solonoid, but he isn't sure that will fix it either.
Honestly, don't bother bringing it to Ford. When this started for me last year, they told me that their solution would be to replace the computer (to the tune of $2k+). Make sure also, that your PVC is ok and you don't need to replace that.
I'm running out of options with mine, and frankly, I'm not sure doing any thing more to it when we can't be sure it's any one thing will work.
But give the unplugging a shot. You'll polute a tad more, but it may stop the problem. Oh, and after you plug it back in, your CEL will go off. But the stalling problem returns after about 400 miles.
My car has just about 123k miles on it now, so I guess it's had a good run. It's just pitifully sad that this is how it is going to potentially end.
