1992 Acclaim with changing idle speed

My wife and I just got a 1992 Plymouth Acclaim. It sat in a garage for about 4 years and has just over 74000 miles. I’ve changed the oil, the plugs, the plug wires, distributor cap and rotor. When we got the car it had about a half tank of gas. We added gumout when we filled the tank the first time. The car has one challenge that was not remedied by the new ignition parts or the gumout. THe idle speed drops suddenly, sometimes every 15 seconds or so. Not a major problem except that it often causes the car to stall when it’s in gear. How do I fix this or what are the most likely causes?

You had to put in a new battery right? If that’s the case, it’s going to take a while for the engine management system to relearn the operating conditions of the engine. So just keep driving the vehicle, and keep refilling the tank with fresh gasoline.