I'd probably start with the basics, whats the Mileage of your Si?
Do you have a lead foot? Either bad driving habits or running too rich.
My first actions would be to run a OBD2 scan & not from a cheap one. Your can can still have codes & not turn on a Check Engine Light.
Unplug the battery terminals to let the computer reset, in the mean time I'd remove the MAF sensor off the intake box & use some spray cleaner from your local auto parts store to verify it's clean. Then let it sit & dry for 20 mins, reinstall.
Again this would be my first approach personally.
Do you have a lead foot? Either bad driving habits or running too rich.
My first actions would be to run a OBD2 scan & not from a cheap one. Your can can still have codes & not turn on a Check Engine Light.
Unplug the battery terminals to let the computer reset, in the mean time I'd remove the MAF sensor off the intake box & use some spray cleaner from your local auto parts store to verify it's clean. Then let it sit & dry for 20 mins, reinstall.
Again this would be my first approach personally.