Something must be wrong, I know you might argue "oh you drive like a maniac" but lets not get into that, I filled up my tank with the correct premium gas, drove carefully not going above 3-4k RPMs for about 80 miles, then refilled the tank and calculated 8.9 MPG. wtf. I get around 23 on the highway, but 8.9 in the city? Something must be wrong with this car. Am I screwed?

my mechanic checked out the sensor levels and they were all correct, so maybe a sensor is broken? or is something mechanically wrong? oil levels maybe?

Do you use alot of A/C... That may be the cause to some extent. My advice would be keep driving and see if it goes up after a full tank. Also you can try some of those fuel injector cleaners from autopart stores.

No AC at all. Would fuel injector cleaners really make that big of an impact? getting half the MPG i should?

Ive been driving for over 2000 miles

Not really sure, all just thoughts. I use fuel injector cleaner every 20-30k with oil changes because I bought my car new. Never really noticed a difference in performance or MPG.

Honestly I am not sure besides laying off the pedal, which you said you already do.. Could also clean your air filter...

plugs

I cant imagine you losing 15 MPG just driving in the city compared to highway. That seems whack but check the air filter, also does your car let you fill the tank all the way? Some people have trouble going over like 3/4

Time for a Tune up? Dirty air filter can cause drop in MPG.

Also filling up after only 80 miles probably won't get an accurate reading with the calculation method. Best to average it out over time on fill-ups (meaning 1/4 tank or below). Time of day, temperature, different gas pumps all affect when the pump thinks your tank is full. So if you're basing 8.9 off this one fill up, I'd try again after a full tank of gas.

i dont see how letting it fill all the way would change anything. I've filled it up multiple times and calculated, all getting extremely low numbers. if it had fluctuated i might consider this but it really hasn't.

can be many reasons...plugs,air filter, proper air in tires, etc

Clean your MAFS. Depending on mileage, it could be your cam and/or crankshaft position sensor. Change spark plugs.

That totally sucks. I sympathize, this must be so frustrating. I will try to help make it as painless as possible, but no guarantees...

Anynigma's easy 6 step method to restoring fuel economy.

1) Check Air Filter, if dirty, replace
2) Check Spark Plugs, if dirty or large gap, replace
3) Reset ECU
4) Reset Idle Throttle Body Position and Accelerator Pedal Position.
5) Clean Throttle Body
6) Take it to a trusted shop and say wtf

DIY's or posts with useful info can be found via search.

You filled up after 80 miles? that's probably the reason why you're getting 9 mpg.

Try driving about 200 miles than recalculating it.

you might want to calculate your gas MPG's by the amount of gallons you put in according to the pump not your gas gauge... our gas gauges are really screwy.