hey i got a stock ej8, i just got a full tune up done except for the o2 sensor done about 2 weeks ago cuz the car has felt sluggish and slow lately. well its the same thing if not more sluggish than usual. any ideas what it could be. im not throwing and CEL's. my alternator belt needs to be replaced and my antifreeze smells like fish so i need to flush that. but other than that there doesnt seem to be anything wrong. it just feels super slow. anybody have idea what i should do. and no turbo, nos or build up ideas. i dont have the money for it right now. plus im getting kinda bad gas mileage too. its like 19 mpg, all city. any help wuld be appreciated.