hey there. im new to this forum but i have a 98 blazer and it ran great but always had a check engine soon light on and when i got it checked it said 02 sensors. so i changed them twice! adn it still wont go off. well one day all of a sudden it started cutting out and running rough and it accelerates really hard adn great but when i try to stick at a steady speed it cuts out and runs awful and when i sit at an idle it will die. i took it to a shop and they said there wasa multiple missfire so they changed rotor, cap. plugs and wires and also did an engine flush and it still ran like crap and they said run it so it all cleans out so i did and it ran really good for almost a day and then back to what it was doing. so i took it back and the shop said it was saying a bad mass airflow sensor and 02 sensors so they changed them and it did nothing and still said bad 02 sensor and mass airflow sensor. does anyone have any idea? any clue or help would be greatly appreciated!

 

also my fuel milage has gone down to about 7 mpg according to my overhead guage.