'91 Buick Regal throttle?

[deletekey]

1991 Buick Regal Limited, 3.8L, 6 cyl., over 100,000 mileage.
When de-celerating as in coasting to a traffic light, etc., the engine "pulses" that it, decelerates, accelerates, decelerates, on and on until I brake to a stop. Sometimes does it while driving a steady speed....anywhere from 25 MPH up.but mostly when my foot is off the accelerator. Second and not sure related problem, when warm weather mostly, it tends to act like it will stall when sitting at an idle at a stop and I put it in Neutral to avoid stall. Any suggestions for either???