Hi, have a high mileage (185k) 2011 Sport automatic. Bought new for my kid to go to away out of state to go to college with and I recall it getting a consistent 33 -35 mpg. Fast forward 12 years and she’s finally getting her own new car and gave the car back to me. Now, it gets an abysmal 18-23 mpg. I’ve changed air filter, o2 (upstream) sensor, plugs, iginition coils and put in fuel injector cleaner to no avail. Any advice on this?

 

Seems like you have covered most of the basics. What kind of oil are you using? What kind of tires are you on ? Size brand and type and what pressures?

 

Check your brakes to make sure nothing is hanging up or dragging

 

Take it to a very technical tech who knows how to use a diag. computer properly. Independent shops who deal with more complex systems... Fuel trims would be where I'd start. If all looks good in the sensor and fuel/ignition management section section, next step would be check compression, leak down test, then check for dragging items as another person stated.

 

I wouldn't have believed this if It was not my experience from a few days ago.

Try cleaning the mass airflow sensor. I track my mpg with Fuelly and it was steady in the 30-32 mpg range for over 7000 miles. Then about 3 months ago it developed a slight miss at idle..... a miss that could pass for the A/C compressor kicking on. In fact that is what I thought it was because the weather got hot at about the same time. The car ran great as always but the idle stumble or miss got worse over time and it wasn't the A/C compressor but the engine never threw a DTC code to run down. My mpg dropped to 27-28. Last week I encountered through my job of delivering auto parts a young kid into building Honda street customs. I asked him about it as he seemed to knew Honda engines really well. He suggested cleaning the MAF sensor as he said a dirty sensor can cause a slight stumble felt only at idle rpms. I did this cleaning then drove the car the next day on a 125 mile loop that that I have done twice before when checking highway mpg. This is about 50 miles of interstate on cruise control at 65 mph then I return on 75 miles of rural two lane 55 mph road with the cruise set at 55.The last time I did this loop I got 42 mpg. The day after cleaning the MAF sensor I got 55.5 mpg on my 125 mile loop. I could not believe the gas pump kicked off at 2.1 gallons. I topped it off with 2.252 gallons. The idle miss is completely gone.

 

what did I you use to clean it?

 

CRC Mass Airflow Sensor Cleaner. It's an aerosol spray and super easy to do. I wouldn't imagine the brand would matter but the CRC name is reputable in other brake cleaner and electronic cleaner products. Follow the directions and don't physically touch the MAF sensor. The spray cleaner does it. I changed the air filter at the same time and it took just a few minutes to complete the job. I didn't believe it would do anything as the MAF wasn't covered with crud or anything but it does have some small passages out of sight.

 

If you're in there anyway, it's good to clean up the MAF, and throttle valve with every few engine air filter changes (depending on your interval), and check around for obviously broken hoses or vac leaks.