Just purchased a PA30. It is having left engine roughness 1400-1800 rpms smooth out above and below uneffected by magneto check, however leaning seems to make roughness a little less... so previous owner has overhauled both mags and all new leads, overhauled fuel servo and divider, new fuel injectors and lines from divider to injectors, new intake gaskets and hoses, overhauled original dual fuel flow gauge(due to no fuel flow indication during startup after servo overhaul).
Now what I've done. All new champion plugs(#4 seemed a little black/rich..not oil fouled) I had them so what the heck. Cleaned injectors like 4 times(no contaminates noted under 12x magnifying)... valve wobble check done(within limits).... borescopes are good, compressions 74/80plus, sniffle valves checked good, engine to magneto timing within limits, new servo to divider hose on the way...

HELP!!!!!!:)

check propellor and governor. Possible that propellor out of balance and roughness shows up in that RPM band. Also possible but unlikely that governor is surging the oil pressure to the prop in that RPM band

Malfunctioning Fuel Flow Divider! Installed a Factory Rebuild Fuel Flow Divider and it Resolved this issue! Smooth running now.