[s-cars] Rough idle?

[Alvin Labonite]

Getting a rough/stumble when given gas at idle somewhere around 1200-1500 rpm. Engine vibrates a little and noticeable. But when tach is below that range and no gas pedal interaction it's smooth and above that range say 1800k and above is fine as well. Car pulls strong and smooth. I haver newer OEM coils and brand new POS.. Coolant temp sensor and O2 sensors are new. One thing I could think of is vacuum leak - but where?