Drastic loss of gas mileage

My gas mileage went from about 20 miles a gallon to 7..? Any advice Please. .it does have a Masair flow K&N installed on it from the previous Owner. .? Clueless

Is the check engine light on? If not it is possible that the mass air flow sensor just downstream of the air filter has been fouled with oil from the oiled K&N filter. Get some mass air flow sensor cleaner and clean it. Do not touch the sensor elements with anything, just spray them and let it dry for a few minutes and reinstall. A bad oxygen sensor can also cause poor mileage, but that will usually light up the check engine light.

Did or has it ever had a complete tune-up Now days people seem to think spark plugs and wires last forever but they Don't

My mileage dropped badly, very badly. I have a 2014 120,000 miles. I purchased a tuner around 80,000 miles, run 89 with a daily driver tune, I was averaging 15.4 on the highway, around 11 in town. Now all of a sudden, it fell out. I am getting 8-9 in town, 12 on highway. Clean air-filter not K&N. What is going on?

I just had my cvt replaced at 70,000 miles. And they talked me into $300 clean the injection system. My on highway mileage went from 23 to 15. ‍♂️

replace the o2 sensors