Geez, just stay out of the pedal for a few days till you burn the gas out. In the mean-time, put in a can of octane booster and take it easy. Mixing a half tank of 87 with a half tank of 91 is how they provide the 89 octane fuel anyway.
You probably have pinging from compression and low octane fuel and the computer is pulling timing. It could have been dirty fuel and if running the gas out and filling with premium doesn't fix it then check your fuel filter for clogging.

warmonger

Former owner of '99 CSVT - Silver #222/2760 356/334 wHP/TQ at 10psi on pump gas! See My Mods '05 Volvo S40 Turbo 5 AWD with 6spd, Passion Red '06 Mazda5 Touring, 5spd,MTX, Black