Wife called me today almost in tears. She was limping home in her beloved Rav4. It wouldn't go above 60 mph and it was shaking and missing something awful. And the CEL was going on and off. Torque lite to the rescue. Code P0303 (cylinder 3 misfire). Switched coils on cylinder 3 and 4 and it threw code P0304 (cyclinder 4 misfire). Have a Denso coil on its way from Amazon. Should I buy a spare or replace all 4 of them? Wife is spooked and doesn't want to have to limp home again. Not that having a spare will prevent that...