Since purchasing my 99 Camry SIX cylinder in 1999, I have used regular unleaded gas, per the manual. The manual mentions how I could get "improved performance" using Premium gas. I stand to be corrected but, here in Canada, I believe the usual 3 grades of gas available are rated 87, 89 and 91 on some kind of octane scale. Last week, when the tank was close to empty, I refilled with Premium gas. This week, when THAT tank was almost empty, I again refilled with Premium gas. So far, I haven't noticed any improvement in performance, i.e. it ran great before, it still runs great.
QUESTION: How many consecutive tankfuls of a different grade of gas does it take before the computer in the 99 Camry "retrains" to the different octane level?