I've had my 350 for almost a year now and recently have been getting around 14-15mpg around town. I mostly drive in eco mode and rarely drive with my foot to the floor.
I used a fuel cleaner, tire pressure is fine, etc. When I first got the car I was getting around 18-20 around town and 21 or 22 on the highway. I only use 91 octane fuel as well.
My car is stock. I also first got the car in new york and now I live in Arizona but higher temperatures shouldn't really be the issue.

Does anyone else see very low mpg with this car or do you think I should look into getting this checked out?

 

"I also first got the car in new york and now I live in Arizona but higher temperatures shouldn't really be the issue."

The higher temps should technically help MPG a little. But are you having to crank the AC more because of the higher temps?

 

When I bought the car it was hot in new york so in both situations the AC was in use

 

I realize you mentioned the AC usage, but realistically I can't imagine someone using the AC equally in both New York and Arizona...chances are you're using the AC longer in the day and year in Arizona...which will impact the MPG.
I live in Ontario which has similar weather to New York and I've been to Scottsdale a boat load of times...there's just no way AC usage is going to compare.

Outside of that, you mentioned tire pressure, which is good to check.

When was the last alignment done on the car?
When did you change the spark plugs?
When's the last time the engine air filter was changed?
Have you changed the PCV valve?
Do you notice the MPG's getting worse as you get closer to the oil change interval?
Have you tried driving around in Normal mode and see what the MPG's is like?

 

This is normal for IS350 mine is also 2014 I only get 16mpg in city no A/C. If I drive in S+ I get only 14mpg, it's abysmal and I can't believe Lexus still using the same thirsty engine in 2021.

 

I'm getting 23 mpg, 95% hwy with AC.

 

This seems to be normal. The previous owner of my 16’ IS300 was from NY and I noticed they were averaging around 14 MPG most likely due to a lot of city driving. I am currently averaging 18 and usually do a mix of city and highway

 

I can definitely get 25 mpg on hwy I got even 27 mpg one time but city is another story.

 

thsts pretty good. My 350 if I start the meter already at speed and only record mpg while on hwy I think it was 28 when I was trying. But 23 is after a couple tanks of gas and normal driving

 

I usually average about 19 in my '14 350 AWD with mixed city and highway driving, but if I'm doing a lot more city and/or getting on it in sport mode, it can drop to 14-15 mpg. I agree that this is atrocious and can't believe Lexus is still sticking with this powertrain.

 

I have never actually calculated the MPG in mine, but according to the display, it says 21.4 since last refuel (1/4 tank left). That's mixed city/hwy, but I drive it pretty aggressively, almost exclusively in Sport+ with traction control off, a/c always on and highway driving is done around 80-85mph.

 

Kind of on the same vein. I just finished changing my spark plugs at 63,000 miles and found all of the old factory installed plugs were gapped small. All were between 0.037” - 0.038” when the proper gap is 0.043”. I will be checking my mpg closely. This has to have an impact on performance and gas mileage. I know the manual says dont gap new plugs but that is just foolish to assume a mass produced item like a spark plug can be accurately gapped at the factory. My new plugs were gapped at 0.040” still small according to spec.

 

2015 IS250 w/ 46K miles - I also thought there might be an issue with gas mpg but I was on the highway (had a bunch of stuff in trunk + a subwoofer).. had cruise on for 70-75 mph.. was getting 27-28mpg. I think it's accurate tbh. Tire pressures were all at 40 psi as well.

 

i drive an immaculately maintained 15 350 FSport AWD. I average a combined 18.8mpg, straight highway cruising I’ve gotten 26.4mpg.
These are by no means a fuel efficient vehicle. Stop n go/traffic/city I’ve gotten as bad as 14-15.

 

These cars get **** mileage. Real bad in town. Lucky to get 16-17 in the city in mine. at 75-80 on the freeway, 23-25 max. IDGAF. Let's be real.. if you wanted good mileage you would not have bought this car.