So i recently bought a 2008 IS250 and i feel like my mpg SUCK!!
The average tank reads about 14.3 mpg and i feel like the needle just keeps droppig. What could be wrong?

 

Spark Plugs, fuel, lead foot, ecu, flat tires, etc...

 

Try resetting the ECU by disconnecting the negative terminal on the battery for 10-15 minutes or removing the two fuses 2-5 minutes . You can also try cleaning the MAF with some CRC MAF cleaner.

Check the service history to see if the spark plugs have been changed.

Try some fuel system cleaner also.

 

That certainly isn't good...Id check the computer against good old math on the next fill up just to spot check it. My '08 IS250 AWD computer has been spot on. The worst I've gotten is 21.5mpg since I've bought it this past June. Best was 31.8 on a 250 mile round trip to the NJ shore....with tons of stop and go traffic. I average 24.5 during my mixed commute on a constant basis.

Check tire pressure (cheap tires can suck up to 1.5mpg also)

Possible clogged fuel injector(s)...try some top end FI cleaner...Amsoil, Royal Purple...Techron...Red Line

Spark plugs.....(PIA to change BTW)

MAF sensor cleaning (easy)

Dirty, clogged air filter ?

 

Maybe need some tune up. My 2008 IS350 get 23.8 mpg.

 

Someone is coming by late at night and siphoning it out?

Seriously, my record low for gas mileage was 17MPG on a tank with winter gas, temps in the teens and single digits, and nothing but short trips. With a mix of suburban and highway driving this time of year, I'm doing more like 23-24. And that's with an IS350.

As other suggested, do a manual calculation to confirm the numbers you are seeing on the trip meter.

 

I usually can get anywhere from 20-30 depending how much I drive on local and freeway.
do you find yourself having to fill up extremely often? with getting 14.3mpg, it seems like you'd be spending most of your time at the gas station

 

Remember in CA they add winter blends. Don't know to how true it is but we all could be losing as well? So if your due for any of the above then try that.

 

My is350 get 15 MPG , I replaced the spark plugs but it did not help.

I use 95 Octane fuel ONLY

 

I second this, I live in NYC and i get 14-17. Why is that? I also drive an is350.
Sparks have been replaces, recalls have been done, all maintenance up to date.

 

Since i have posted this i noticed that my mpg has increased tp about 20mpg. Someone told me it was probably because the ecu had been reset and it was still not used to my driving habits. Not sure at all on how true this is though.
..