Dropping Miles Per Gallon

[cheukfu]

I have a 96 C220 and living in Honolulu, Hawaii. My car usually gets about 300-340 miles on a tank before. But recently, it has been dropped to only about 250-270 miles. I think it has something to do with my school and work schedule because I stuck in really heavy traffic almost everytime I drive. But my gas mileage seems to keep dropping, so can anyone tell me what would lead to less MPG? Or anything I can do to increase it?

P.S. I just had my air filter changed. But I haven't change my spark plugs for like 2 years, and I just changed one of my rear tire because it went flat and now it had different tract with others. Also I reset my tranny communication with the ECU (Using one of the techniques someone provided here). Does any of these things affect my MPG? Appreciate your help!!

['91 300CE]

Traffic will have a huge impact on economy... also if HI requires E-10 gasoline (10% Ethanol) you will lose MPG's as well...

[benz rider]

I'm losing at the pump too and I thin kit may be the fuel filter. that's what i'm starting with. you should try that next. I always start with the cheapest repair first.