Just bought a 2000 celica gts. Wanting to know what you guys think of this. Before i bought the car i asked the dude a few questions, what oil did you use in it? He says hes been using castrol 10w-40. What octane does the car take? He says i have always used 87 octane. The car has 123k miles on it, he has had it since 100k. You guys think using this octane has hurt the car any? What about the oil? I noticed on the oil cap it recommends 5w-30 so i changed oil with that type. Should i continue to use 87 octane or move up to premium? The car had CEL on and i had it checked it was system too lean and catalyst system efficiency below threshold. Air box wasnt clamped correctly so im guessing that was system too lean. As for catalyst im guessing using 87 octane for 20k miles has something to do with that? I reset the CEL and it has yet to come back on and has been drove around 150 miles since then. Any help would be GREATLY appreciated!