[shorod]

Well, a plugged fuel filter would not typically contribute to high fuel consumption. It can however accelerate wear on the fuel pump (backpressure loads the pump motor).

Disconnecting the inertia switch definitely cuts all power to the fuel pump motor, but at idle the engine will run for much longer than most people would expect. I doubt you did any damage with what you did. If the battery is old/weak, I'd suggest you get that replaced before you worry much about the fuel consumption and way the engine runs. Many newer cars are so dependent upon the electrical system that an old battery that load tests fine can still cause odd driveability issues.

-Rod