KTuner.com

So I put in a K&N Cold Air Intake, a Mishimoto Intercooler and did a custom tune through ktuner. I didn’t do anything egregious with the tune. Deleted rev hang, factory throttle padding, 21 psi, moderate throttle pull, improved launching, etc. Not knowing what to do with the mass air flow settings, I set it to PRL cobra’s cold air intake, assuming that setting will account for the K&N CAI better than nothing.

Before everything, I was getting 33-34 mpg, now i’m getting 23. There is no way in hell a CAI is throwing the MAF off that much and I am definitely not having a lead foot. Where did I go wrong?

This is a 2021 Hatchback Sport Manual

You chose the PRL RACE MAF and don't have one. You assumed wrong.

You don't want to change the MAF settings unless your changing the MAF housing. Did the K&N you got connect to the stock MAF housing, or did you have to remove the MAF sensor and install it into the intake somewhere?

If there's a difference in the diameter of the MAF opening between the K&N setup and stock, then K&N support may be able to help with MAF scaling. Otherwise you would want to go back to the factory MAF setting and do some logging to see what's going on.