Stalling Chev Celebrity

I have an '88 Chev Celebrity, 2.8 V6 (MPI) - 370 K km. It is stalling more and more often frequently - more pronounced when cold, but even when moderately warm. The Engine Check light comes on and stays on (the first time I have seen it come on in the 15 years we have had it) The motor seems to "chuff" and splutter- pulling out of the driveway requires about 4 restarts of the motor. Get to the lights at the end of the road and it stalls again. It runs normally once I am moving on the highway and has the usual amount of power.
I changed the plug leads and plugs, and replaced the air filter last week -all to no avail.