Hi everyone,

I am sure this topic probably has been beaten to death here, but I am hoping someone can shed some light on what could be wrong with my car.

I picked up a used 2017 IS300 F SPORT AWD last year, and I've noticed I'm getting way worse fuel economy (17L/100km or 14 mpg) than what manufacturer posted (12.2L/100km or 19 mpg) for city.

I understand this car isn't great on fuel, but that's a 40% increase over what's posted.

I took the car in for checkup, no errors, nothing is wrong, they even ran some fuel economy diagnostic, and to my surprise, they said I was heavy foot.

I understand everyone has their own perception of whether they're heavy foot or not, but I am confident I'm not, and I can even post a video of my driving habit and how my rpm changes.

With that in mind, is there anything else that could have caused the poor fuel economy?

 

If you idle a lot, that'll tank it (remote starting)
Some people say drive in Normal mode versus Eco because Eco makes you press on the accelerator more
Inflate your tires cold to 40psi
Driving on highway, put it in cruise to get the most efficient mpg as possible
Take unnecessary weight out of the car

Just some things I do

 

Personally I wouldn't over-inflate the tires.

I think it's highly dependent on your driving routines. I saw about 19 MPG over the lifetime of my ownership in my 2016 IS 300 AWD, with about 60-70% driving in the city. On longer highway trips I could get it into the high 20's. What really tanked my fuel economy was winter driving. Remote-starting, babying the car, winter-grade gas... all those things combined would drop my fuel economy down to about 17 MPG in the winter.

 

my 2015 350 AWD FS averages 11.2L/100km combined.... driving normal with some spirited driving....idling KILLS economy, bumper to bumper/city traffic also tanks it. Quite a bit worse in the winter.

You can try resetting the ECU, checking tire pressure, checking engine air filter etc....I also noticed using Top Tier certified gas stations gets me an extra 10% fuel economy.

Do all that, reset ECU, track mileage and go from there.

 

Thanks a lot everyone! Didn't expect to get response this quickly.

To respond to some of the suggestions:
idling - I basically cut down my idling to only when I'm driving, if I'm parked, I turn off my car regardless. I tried that for two tanks of gas and didn't notice any difference
weight - I would say my car is pretty empty
highway - unfortunately, my daily commute does not require any highway. It's all city driving, and rarely in traffic jam at all (although some time I take side road to avoid constructions, so I'm not sure if that could attribute to the high gas mileage due to more stop and go)
tire pressure - something I could definitely check, I'll make sure it's up to manufacturers spec

ECU - the one thing I haven't tried so far, the dealership suggest I do that, and seeing that it is being suggested here, I'll give it a shot.

Again, I can't say thank you enough for all of you responses. It's just one of those issues where I tell people and they immediately conclude I go pedal to the metal at every red light, or just have very heavy foot.

 

Consumers tend to think that the large black numbers on a car's window sticker, which list the EPA estimated fuel economy rating, are what they will actually get while driving that car. Unfortunately, this is another situation covered by the saying, "Read the fine print." The fine print says, in essence, actual mileage may vary depending on a whole lot of things.

THe EPA doesn’t test every new vehicle for fuel-efficiency. Only 10 percent of vehicles end up being tested, and most of these are selected randomly. For the vast majority of cars, the EPA relies on the automaker’s provided estimates. Each manufacturer tests its own vehicles.

 

I'm averaging anywhere between 9 to 22 L/100km with my 2018 350. It really, and I say really, depends on the kind of driving and city/hwy mix.

With covid work from home, all I do is short trips to the school and back, mostly going to max 3rd gear so the car has enough to warm up, that kills mpg! lol!

 

Also when they say cold tires it can be that the car was sitting for at least an hour and the trip to the gas station to fill air in the tires is less than 1 mile going at moderate speeds. At that you consider the tires cold but once you "warm" them up going between moderate to high speeds over a mile just add 3-4 psi once you start filling the tires. Forgot what video I was watching that explained this but this helped me get more mileage.

But really it all depends on the speed you drive at, since my commute is mostly highway now (~25 minutes). My MPG sits around 20-26 MPG versus I was getting between 14-18 MPG when my commute was city (~5 minutes). This is all on ECO mode and I try not to go over 2500 RPM if I don't have to. I readjusted how I drive in traffic and don't try to speed up to close up the gap between me and the person in front of me and leave about 2-4 car gap now. I also adjusted my habits to where I make smart lane change decisions that allows me to slowly speed up without having to slow down. I thought my driving habits weren't bad but after adjusting to clam the heck down on the road, I'm getting better mileage.

Always use Top Tier certified gas if you can. I think Costco is considered Top Tier too if you have a membership. Texaco is my go to since the price isn't so bad and it's one below Shell. You can also use a fuel system cleaner too and you might get better range but it's kinda like snake oil to some. I also think the whole "warm" up thing is nonsense on modern cars, as long as you wait till the initial high start RPM goes down to "idle" under 1000 RPM you are good to drive off. You can tell when the car is ready by feeling and hearing the car.