So here is the problem ! I used to get bad gas mileage around 21-23mpg highway (note: i have had replaced the coils,plugs and injectors already ) i replaced my maf sensor and it restored my gas mileage to 27-28mpg on highway for some days but now again i get just under 23mpg so i tried to drive the car with the maf disconnected and surprisingly it went back to 28mpg like Wasn't it supposed to run rich with the maf disconnected ?? Obviously my car stalls At first start and jerks when i floor it because I unplugged the maf but i get better gas mileage so can anyone explain me what could be the issue ?!

 

How are you calculating MPG? If you're using the MPG displayed on your dash it isn't always correct, mine always reads high after I reset it and then goes back to a more normal 23-24. To do this test correctly you need to fill your tank, drive the car and note how many miles you travelled then fill the tank back up and calculate your MPG from that.