I ran midgrade for a month now my car lacks power. The valves were rattling bad til the 89octane burned out(i filled up on 93). I replaced a bad idle control valve and then my car lost power the next day. I replaced the spark plugs and fuel filter now my check eng. light is on. It looks as if the HB pulley is warped also. How do you diagnose a bad harmonic balancer? I don't really think its the plug wires. The coil pack and DIS are good. Im going crazy! Any help is greatly appreciated.