1994 Oldsmobile LSS idle problem

Hi car pros. I have a 94 oldsmobile 88 royal lss that has a little mis to the engine. It is more noticable at a idle in park. And when acclerating you can see the rmp needle bouncing slightly. But cant feel it in the car. But you can hear it in the engine.I have replaced all three coils. The board the coils are on. Forgot what the was called. Um plugs, wires, fuel pump, both fuel filters, mass air flow sencor, o2 sensor and air filter. None of that helped. And checked for crack hoses for a vacum leak and all check out good.O and I put a egr valve on it but it didnt help so I took it back and got my money. What do you think my problem is?