I own a 1995 Buick Roadmaster Wagon. It has approx. 137,000 miles. It has an LT-1 Corvette engine in it. It has always performed great on gas mileage. Usually 28 mpg on the highway and nothing under 23 mpg in town. I drove it on a 400 mile trip and got 28 mpg. Came home. My husband changed the air filter because we changed the oil and had not changed the air filter recently. I filled up and drove and gas mileage dropped to 10-15 mpg. I drove the tank out and filled up again, same thing. We checked tire pressure. Filled it up a 3rd time and still 15 mpg. It runs smooth. Starts fine. I have not changed gas. I go to the same gas station that has the best gas and all my cars run terrific on this gas. It is not ethanol. It is 93 octane. I have not checked the fuel pump yet, but could it just have an immediate effect like that. The only think different was the air
filter. Any ideas?