Reason for poor fuel economy

[anokES]

Whats a typical reason for poorish fuel economy? What needs to be replaced to get it back up to normal - I know driving habits can completely change but that's not what I'm talking about, I also know replacing the O2 sensor can help but what else?

[jlevie]

Intake leaks, a fuel system problem, injector problems, valve adjustments and condition, ignition problems or bad/wrong plugs, ECT sensor problems, AFM problems, a bad DME, and low compression. And on an ETA engine the cold start system. Singly or in any combination can reduce fuel economy.