I picked up an inoperable A1316 with what turned out to be a backlight issue. I was able to resolder the LED backlight...

Sounds like a misfire but it’s hard to say without knowing more information about the circumstances and environmental factors when this began occurring. Do you have any other info you could provide? And just a heads up….Amazon and eBay both have very inexpensive OBD2 scanners for sale (<$30) that will allow you to connect to your car’s computer so you can read the trouble codes and hopefully correct whatever is causing it to do that

Many things can cause high fuel consumption, it’s generally not a quick and easy diagnosis. Anything from low tire pressure or worn out tires to your air/fuel mixture running too rich (too much fuel) or lean (too much air). It can be caused by improper alignment, dirty sensors, exhaust or intake leaks, engine misfires, and improper brakes. Further, operating conditions can cause low MPG as well; frequently accelerating very quickly, riding the brake, incorrect fuel type for the application or it can be caused by your cars computer in certain (unlikely) situations. There are other things that can cause it as well but you get the idea. If you fill in a little more info about when this started happening, the circumstances concerning your car at that time, environmental factors and any other pertinent data you can think of, I will try to help you narrow it down a bit