I have a 2002 Pontiac Montana

I have a 2002 Pontiac Montana. A few months back we replaced the idle air control because it was not wanting to stay running (stat sometimes and not others), but it ended up being the MAS was unplugged (no ideal why or how). It has run perfect ever sense until last week. On Saturday the 2nd it drove perfect about 45 minutes from home, we went in a did what we were doing for about 4 hours, came out and it would not start on it's own without giving it gas and keeping your foot on the gas. I had the battery tested (it had obviously leaked) which was bad so I replaced it, but it did not fix the issue. I took it to a couple mechanics to look at it, but they said they had no idea what was wrong. Over the past week it was a little better, if you started it by giving it gas and continued to keep the RPM's up to about 1500 for a minute or so it would stay running. In park or at a stop they would drop to about 500 and the fan for the heat would die, but the van would stay running. Then on Thursday night it started acting really bad, it dies every time you take your foot off the gas, instantly the RPMs drop to zero and there is no recovering it. It starts back up if you give it gas and keep the RPMs around 1000. A couple times that it died, it reset the clock in the van and made the ABS light come on for the duration of that trip. You can hear the fuel pump running and when it dies the fuel pump is still running then it cuts off, yesterday (Sunday) I took it in and had the fuel filter replaced, but that did nothing. The guy who replaced the filter said when I start it it sounds like a bad coil pack, but I get a spark on all 6 cylinders. I am at a loss as to what to do next, it runs great as long as you keep the rpms up above 800.