My 95 Pontiac Bonneville Is sucking gas way too fast on 1995 Pontiac Bonneville

It is like 3 mpg

Asked by for the 1995 Pontiac Bonneville
3 MPG is horrible. The engine coolant temperature switch may be reporting the engine is stone cold, making the computer add fuel all the time, a fuel pressure regulator may be leaking, fuel injector may be leaking, air filter restricted, perhaps a mouse has built a nest in the air filter housing restricting air into the engine. It shouldn't be hard to make improvements. 3 MPG will quickly kill the catalytic converter.