Well if its white it could be C/O not right, iirc I had an xr3i efi, used too white smoke almost like condensation in system, turned out co adjuster were shot...

New adjuster, no white smoke long chalk but worth a note imop..

Pull plugs and check no crystallized deposits on electrodes, indicating coolant getting in too system, when u had rebuild were head pressure tested and skimmed to be sure all well?

U sure all ya coolant circuits plumbed up right, heater working hot cold, oil breathers ok, no mayo deposits? Thermostat working?

Is turbo water cooled...could be a crack inside leaking into exhaust side..

Also id drop a bit of the oil out an check no water getting in as could be a crack internally..

Such a hard thing to diagnose, but if its running OFAB/FAC with a chip id get it checked over asap if your sure all I well elsewhere as these generic chips can be a nightmare if just slung in..