1990 Pontiac Gran Prix, 3.1L V6, Automatic with 100k Miles
Car sputters when idling, sometimes dies and has trouble restarting. Has very low power running, even with foot on the floor. When on the gas, car shakes until throttle is about half. Doesn't shake between half and full throttle, also doesn't shake when off the gas.
I want to say the shaking has something to do with the transmission, because it sometimes shifts really hard.
But the really low power, sputtering and dying is my main worry. I inspected the spark plugs, and they are fine. Fuel and Air filters were replaced, but neither one was in bad shape (could blow through fuel filter and see through air)
Where should I go from here to solve these problems?