rough idle and poor fuel milage after tune up
i changed the air filter, fuel filter, plugs and wires a little after i bought my geo tracker and i was getting 29 to 31 mpg. now after the tune up a check engine light came on and only gets 24 mpg top and has a rough idle. i changed the o2 sensor thinking it was bad but not the answer. a guy flashed the CEL and it came up rich/ lean either air or fuel dont remember what the book read. what can i check next?