Per the manual, my '99 GS300 requires minimum 91 octane gas. I recently filled it with 87 (on the phone, wasn't paying attention) and didn't really notice much of a difference. No knocking or pinging. Anyone else running 87, and what is the long term effects ?

No effects. You're fine.

The engine will retard the spark if it detects pinging. If you really jump on the accelerator you could possibly detect slight less power due to the spark retard but you will likely not even notice it.

I used to run premium until it hit $.50 a gallon back in 08. Then i switched to 89. Noticed no change in power or mpg. About 6 months ago I started running regular since Sam's only offers 87 and 91 octane. Still no change in mpg. I don't run it hard enough to notice any performance affects.

JimA