Here is something I found on Allpar thats sounds like your problem.Hope this helps.
I've read many notes and postings regarding Mitsubishi 3.0 motors with a chronic, but intermittent stalling problem when coming to a stop. No codes, no temperature correlation, no weather effects, but it seemed tied to the fast idle servo located in the throttle body, which I had looked at before and saw nothing unusual. Starting with the new 1988 Caravan, I have owned and repaired five 1988 Dodge and Plymouth Vans (Caravan and Voyager) over the intervening years totaling some 400,000+ miles in aggregate. Three had stalling problems at one time or other when coming to a stop. I even placed a pressure gauge in the fuel line in an attempt to blame the fuel pump. I broke a transmission trying to get a stalling motor going on ice and I have to admit that I never really knowingly cured this annoying characteristic until now.
I ran into an independent garage owner and race car builder one day who seemed to be quite familiar with the stalling as I described it. His hint galvanized me to take another look at the servo. He suggested that it was sticking (tight clearances in the cone valve area) due to the smog debris. He was right!
I had heard of that sticking before in connection with gasoline varnishes or deposits, which I dismissed because I knew that no gasoline was in the the throttle bell area; but the deposits, deposited in the valve by smog passages that share the valve passages, act in a subtle way, likely affected by combinations of moisture and temperature, in a stick/slip kind of way. The result was seemingly random and frustrating, as it would manifest itself at the most awkward moments, like in the middle of an intersection waiting to make a left turn.
It's been several months since the stalling. It ended immediately after solvent cleaning the fast idle servo as I indicated. (don't get solvent in the motor actuator). I hope this is helpful.