this 97 accord was down to 19-20mpg this winter from 23-24 last fall. I thought it was oxygenated fuel. Then I took it to dealer last month who changed spark plugs, wires and also seals for spark plugs ( they had some oil on them). Now the mileage went to 21.5 mpg (mostly local driving). On a all highway trip it was 31 mpg. Does that sound ok in local driving.? considering highway mileage is good, should i be concerned. Before winter, I had the timing belt/ water pump and radiator changed. it has 80k miles.