1989 GMC Jimmy stumble

I bought this new and have always kept it in good shape and serviced at proper intervals. It now has 140,000 miles and runs great - except for a “once in a while” problem.
When taking off from a stop, it will stumble just for a nano second. Before I can even raise my foot off the throttle, it takes off! Then it won’t do it again for weeks or even months.
It has a new fuel pump and the throttle body injector has been worked on. In desperation the mechanic replaced the distributor. That seemed to solve it for about 6 months. Now it is back to a very random occurrence, always when taking off from a stop - never when going down the road.

The problem might be due to a faulty MAP sensor.


The MAP sensor took the place of the accelerator pump and the vacuum advance when engines had carburetors and distributors.