Soot/Solids/Insolubles include ash, carbon, lead salts from gasoline engines, and oil oxidation. We have plenty of Toyotas over here with 1.5L 1NZ-FE engines. They are speced for 95 RON or higher gasoline (probably 89 PON in USA), so dont use anything lower. Another difference is that you have EGR in your 1NZ-FE while we dont. VVTi + EGR, more exhaust gases are recycled back in to intake, not good if you ask me. I would use the best fuels available, maybe Chevron 91 + techron regularly to keep the cc clean. ARX definately sounds like a good idea esp if you dont know the previous history. Maybe even 2 ARX cleaning phases. Sustained high speed driving & hill climbs also puts more stress on an oil and increase chances of sludging problem. Some oils have very good cleaning ability and will help prevent sludging. Dyson in-house kits still use 'soot/solids' readings and oils like Castrol SLX aka GC consistently give me zero soot/solids. In my opinion, the new generation of Toyota VVTi are even more prone to sludging than the previous generation of non-VVTi engines. My 2.4L 2AZ-FE runs very hot compared to my 2.2L 5S-FE. I also have a 1.6L 3ZZ-FE, but does not run as hot as the 2AZ-FE. I was considering the 1.5L 1NZ-FE too, but bcos it uses electric power steering, I decided not to get it.
