My 07 owners manual recommends 89 octane. It says 87 can be run if no knock s experienced and that 91+ is not recommended for use.

After any mod or engine maintenance like spark plugs its a good idea to disconnect the battery. The computers do "learn", but disconnecting the battery puts it directly into an accelerated learn mode. After a period of driving time the algorithm slows so it takes changes to the system longer to propagate.