1997 Plymouth Voyager engine idling

Many times (not always) when I slow down to come to a stop, or take my foot off the gas to coast, the car stalls. I can feel a shift in the transmission at the same time. This has also started happening even while at highway speeds (60-70 mph). I can put the car in neutral and turn it over and restart it generally right away (sometimes it takes a few tries). When this happens the "Check Engine Light" comes on. I have had my mechanic scan the tranny, to no avail - nothing turned up. For a while, it seemed that if I kept the A/C running the car didn't do this as much, but that doesn't seem to be as effective now. I have been told by somewhat car savvy friends that it could be the "Idle Stop Solenoid" or a "Mass Airflow Sensor". For the latter, I read that these cars do not have them.
Oddly enough, my father has the exact same car, bought in a different city, just five months after mine. He has only 75,000 miles on his, but it is developing the exact same problem.
I can be very disconcerting, as it also sometimes stalls just after starting to accelerate out of a stop, meaning it stalls in the intersection.
Any ideas?