Bro I myself faced this same issue.
And Alhamdulillah it resolved but not in the first place.
I don't know the "exact" solution tbh but I can write down the things I opted for.
- Coils ( I didn't change mine even some of them are covered with tape but bad coils can cause leakage of current and will affect your performance meanwhile average.
-Spark Plugs (Use only recommend spark plug, spending lots of money on double tips or other expensive plugs isn't going to help you)
-EGR Valve (clean your EGR valve, It might help you as I did the same when I was facing this mileage issue, A stuck EGR can also have adverse effects)
-Oxygen Sensor (Make sure that the one you installed is all good/ try installing your previous oxygen sensor after cleaning).
-Go for a complete tunning I.E tappet adjustment (if required), Complete throttle body service incl. Sensors (with Sensor cleaner only)
And I'm assuming that your engine is all good, not reducing oil, no smoke etc!!!
Check Fuel Tank Cap
Check fuel leak
Check Vacuum leaks
Try to change gear below 3 Rpm
Drive-in low Rpm
Avoid A/C while idling or in traffic.
Here's my 2 cents, many other seniors can guide you a lot better!
Thanks
