I have honda civic 98 with D16Y4 engine and auto transmission.I'm getting low mileage 9-10km/L without a.c, driving with light foot with rpm between 2k-3k. I avoid long idling, drive within city usually heavy traffic using engine oil 10w-40 Liquimoly. Cleaned O2 sensor with this methodcheck here, changed fuel filter, air filter but haven't gone above 10km/L. Tried 93RoN but it makes no difference used 87RoN normally. I keep tyres pressure at 30. How come I get better mileage ? There's no issues with car other than mileage issue. Suggestions are welcome
That actually doesn't sound that bad - it's actually pretty much what the book figures suggest for that car/engine combo during urban driving.
So I suspect you may be chasing a non-existent problem.