1988 Chevrolet Celebrity RE: car problem

OK its a 1988 Chevy Celebrity, has just a little over 98,0000 miles on it now. The car is acting funny and I cant figure it out. It starts with no problems but idle seems a little high and will flux up and down while in park. If I don't let it sit and run for a few min before driving it then it will stall out. It doesn't matter how soft or hard I hit the gas pedal. It will sometimes do this while driving and acts like its losing power. Not burning oil, changed plugs and fuel filter so far. I run Lucas complete fuel system cleaner in every tank since I got the car to help clean it out. Air filter needs changed but not bad really. Whats causing this? I cant find a vacuum leak anywhere. This is driving me nuts and want to get it fixed so I can move on to other things.