starting problem

we have a 2002 jeep grand cherokee limited 4.7 V8. For the past few months we have
been having a problem with it starting. Most of the time (esp when its cold out) if we
start it it will start for just a second and then die. Then to get it started we have to keep
our fod on the gas..once that happens we have to keep our foot on the gas and slowly
let off until the idle catches on its own. Sometimes this works but a lot of the time it
dies again one we back out of the driveway and take our foot off the gas. So we usually
start it again the same way and then it'll die one or two more times in the neighborhood
before we get on a main road. Once it gets going it still freak us out because once we
let off of the gas the rpms will drop to almost 0 and then catch back up. We have
changed the throttle position switch, IAC, and O2 sensors and checked all of the
hoses. We are getting desperate. I've seen some people talk about the crankshaft
sensor and the PCM, but all of those forums never really sounded like our exact startin
problem. We would really appreciate some insight from anyone willing to help!! Please!