Engine Performance problem
2003 Chevy Monte Carlo 6 cyl Front Wheel Drive Automatic 87000 miles
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My car is spitting and sputtering like you have got a hold of bad gas. but we filled the car up and put a gas treatment in it and it still is doing that. Is there something that I need to do when it reaches a certain mileage. Is there something wrong with the computer, or maybe sensor that may be going wrong. Thank you lynn Lester

First thing I would do:

check for codes in your computer, even if the MIL is not on.
It could help narrowing down possibilites.