Poor City Fuel Economy

[si2ki30]

My 2000 i30 has been getting some pretty bad city mpg's lately.

Some weeks, I do about 95% city driving and it hovers around 12mpg average. (6 mile twice-daily commute with some lights, small hills, NO traffic)

But, when I take road trips between states, I'm getting 28mpg average with 95% highway driving.

I'm not especially aggressive in my city driving and the car is in great tune with the following stuff:

no codes EVER
oil change synthetic 5w30 every 4000 miles
new plugs
new coils
new air filter
new coolant temp sensors
new knock sensor
new maf sensor
new thermostat
new water valve
new rad cap
properly inflated 205/55r16 tires


Is there anything on the engine that typically decreases MOSTLY city mpg's when it's faulty or failing? sensors, cats, etc?

[maxhopper]

My mileage has taken a hit with the winter weather due to the fact that I let my car warm up for a while prior to driving. Also, usually the cooler the intake air charge the more fuel you will burn.

There could be other issues going on with your car such as O2 sensors, or restricted catalytic converter that could affect the mileage, but normally those items would tun on the check engine light.