Problem upon startup?

I drive a 1998 Ford Mustang. Last week it started sounding like it was choking out upon startup, but giving it a little gas seemed to fix the issue, and it settled down. Once the vehicle was on the road I took it to a mechanic who hooked it up to one of those under the handheld dash diagnostic machines which said no codes popped up, my check engine light burnt out a while ago so nothing popped up on their system initially. I asked one of the mechanics to drive it and I went with him, he drove it around for about ten minutes, he said it ran fine, the chugging might be a o2 sensor (I have had at least one of those changed since owning the vehicle) instead of checking to see if one of the o2 banks is bad he said to come back if it went out, as If that would help! Anyways they said it was fine, but as soon as I started it up to drive home it went choke chug choke chug and the car shut off. One of the other mechanics looked at it after hooking it up to their computerized diagnostic machine and said a code popped up, but then he cleaned the dirt off some part and told me to get a new air filter whenever possible. It seemed fine once I initially drove off, but I did not quite trust it so I had a relative drive it home for me while I followed behind. Once again it made the chug chug noise and felt like it was not getting fuel according to the relative. I need help potentially diagnosing it so that when I take it in to yet another mechanic, one who is hopefully competent I might have a better idea of what could be causing the issue.